Add ability to build GnuCash with CMake

Backported from master.

cmake/README_CMAKE.txt

@@ -0,0 +1,218 @@
+Using CMake to build GnuCash
+============================
+
+== Intro
+
+As part of his CuteCash work, Christian Stimming added support for
+using http://www.cmake.org[CMake] to build the part of GnuCash that
+went into CuteCash. This work extends the use of CMake to cover all of
+GnuCash proper such that GnuCash itself can be fully compiled with
+CMake.
+
+Some advantages of using CMake:
+
+ * The build time on Windows drops from around an hour to just a few
+   minutes.
+   
+ * CMake supports the generation of build files for several IDEs
+   such as Xcode, Eclipse, KDevelop and others. The open source Qt
+   Creator and the commercial CLion C/C++ IDE from JetBrains can use
+   CMake files natively.
+
+ * The CMake language, though with significant issues, is still
+   easier to maintain than autotools.
+
+This setup also uses the http://www.ninja-build.org[Ninja] build
+system to enable fast and parallel builds on Windows. (On POSIX
+systems [OS X, Linux, FreeBSD, etc.] Ninja does not seem significantly
+faster that using the default Makefile generator to me.)
+
+== Scope
+
+The scope of the current work is to duplicate the `make` and `make
+install` actions as the Autotools system would. Currently, there is no
+support for `make check`, `make dist`, `make distcheck` or similar
+targets. Other limitations include:
+
+  * Not all options available in `./configure` have been ported to
+    this CMake system.
+
+  * Password management is included for OS X, but not
+    tested. Gnome-keyring and libsecret support has not
+    been ported over.
+
+  * The Xcode build only supports the Debug configuration. Others such
+    as Release are not supported yet.
+
+  * Python support has not been ported over.
+
+  * Visual Studio support is out of scope. While CMake supports
+    generating build files for Visual Studio on Windows, it is not
+    likely at this point that either GnuCash or all of its
+    dependencies can be built using the Microsoft compiler tool chain.
+
+== Known Issues
+
+* Sometimes the Tip of the Day is empty. I've got a stray
+  carriage return somewhere.
+
+* Clicking on 'Start AqBanking Wizard' in the AqBanking setup will
+  cause a crash. I have not yet investigated this.
+
+== Using CMake on Linux, OS X,  etc.
+
+=== Prerequisites
+
+The CMake setup does not support building and installing dependencies
+(although it probably could some day). So you need to have the
+dependencies available, most likely by having run the existing
+Autotools build at least once. Various resources on the GnuCash wiki
+will have advice on how to do this.
+
+You will need to have CMake and optionally Ninja installed, either
+from distro package repositories or by hand. You need at least version
+3.1 of CMake.
+
+=== Running CMake
+
+The next step is to invoke CMake to generate the build system. Before
+running CMake, you need to create a build directory:
+
+  $ cd ..   # back to workdir
+  $ mkdir gnucash-build
+  $ cd gnucash-build
+
+Then decide what cmake command line options you will need:
+
+ * If you want to install after building, add
+   `-D CMAKE_INSTALL_PREFIX=/path/to/install`
+
+ * If your dependencies are installed in a non-standard place as is
+   typical for building on OS X, put
+   `-D CMAKE_PREFIX_PATH=/path/to/installed/depends`
+   on the command line.
+
+ * If you want to use the Ninja generator, put `-G Ninja` on the
+   command line.
+
+ * If you want to use the Xcode generator on OS X, put `-G Xcode` on
+   the command line.
+
+ * If you don't specify a generator, Makefiles will be generated.
+
+ * Finally, put the path to your source directory last.
+   Here, that is ../gnucash
+
+ * There are other options available; look in the `OPTIONS` section of
+   the top-level `CMakeLists.txt` file.  For example, you can disable
+   SQL using these options.
+
+Some examples:
+
+ * Build on Linux, don't want to install, use the Makefile generator:
+
+   $ cmake ../gnucash
+
+ * Build on Linux, install to /tmp/gnucash, use Ninja generator:
+
+   $ cmake -D CMAKE_INSTALL_PREFIX=/tmp/gnucash -G Ninja ../gnucash
+
+ * Build on OS X, install to /tmp/gnucash, use Ninja generator:
+
+   $ cmake -D CMAKE_INSTALL_PREFIX=/tmp/gnucash -D CMAKE_PREFIX_PATH=$HOME/gnucash-unstable -G Ninja ../gnucash
+
+ * The same, but use the Xcode generator:
+
+   $ cmake -D CMAKE_INSTALL_PREFIX=/tmp/gnucash -D CMAKE_PREFIX_PATH=$HOME/gnucash-unstable -G Xcode ../gnucash
+
+=== Building
+
+The Xcode, Ninja and Makefile generators all support parallel builds,
+so decide how many cores you want to use.  Ninja will pick a sensible
+default.
+
+If you chose to configure for installation, you can use the `install`
+target for each generator. The Makefile and Ninja generators also
+support a verbose option if you want to see all of the command lines
+scroll by. Xcodebuild seems to show all the gory details whether you
+want them or not.
+
+For Ninja, use the line below. Note that the executable is called
+`ninja-build` on Fedora. Also, Ninja supports the `NINJA_STATUS`
+environment variable to give status on the build. I like to use
+`NINJA_STATUS="%es [%p/%s/%t] "`.
+
+   $ ninja [-v] [install]
+
+For Makefiles:
+
+   $ make [VERBOSE=1] -j N [install]
+
+For Xcode via the command line (see below to build from within Xcode):
+
+   $ xcodebuild -jobs N [-target=install]
+
+=== Launching GnuCash
+
+Assuming the build completes successfully, in all cases you can run
+directly from the build directory:
+
+   $ bin/gnucash
+
+In you chose to install, you can switch to the install directory and
+do the same.
+
+
+== Using CMake and Ninja on Windows
+
+
+For Windows, follow the instructions at
+https://github.com/Gnucash/gnucash-on-windows to the point where you
+are ready to run install.sh.
+
+Edit custom.sh to add these lines at the bottom:
+
+  WITH_CMAKE=yes
+  WITH_NINJA=yes
+
+Ensure that your custom.sh file contains this line:
+
+  MSYS_DIR=c:\\gcdev\\mingw\\msys\\1.0
+
+Remove or move any existing install at /c/gcdev/gnucash/inst.
+
+Then continue to follow the existing build instructions.
+
+At this writing, generating a distribution with the CMake build
+via dist.sh has not been tested.
+
+
+== Using Xcode on OS X
+
+CMake can generate build files for Xcode such that GnuCash can be
+built, run and debugged from within Xcode.  Follow the instructions
+above to the point where you would use `xcodebuild` to launch the
+build. Instead, launch Xcode by doing:
+
+  $ open Gnucash.xcodeproj
+
+Xcode 7 will pop up a window about Autocreate Schemes. I usually
+choose "Manually Manage Schemes". On the next window, use the "\+"
+symbol to use the "ALL_BUILD" scheme. Then click on OK. If you want to
+be able to run the equivalent of "make install" from within Xcode, use
+the "+" symbol again and choose the "install" scheme.
+
+Back in the Xcode main window, make sure the "ALL_BUILD" scheme is
+selected (next to the stop symbol).  Click on "ALL_BUILD" and
+then "Edit Scheme". On the "Info" tab, choose the executable to be
+"gnucash".
+
+Now use Command-B to build (or Product -> Build) to start the
+build. When it finishes, click on the play symbol (or Product
+-> Run) to verify that you can launch GnuCash from within Xcode. If
+that works, you can now set breakpoints with Xcode and debug away.
+
+To run the install script, click on the "ALL_BUILD" scheme and change
+it to "install". Then press the play button to run the script.
+
+That's it.