AM_CFLAGS is passed both to the compiler (.c -> .o) and to the linker, so it
should only have flags that are appropriate for both steps. AM_CPPFLAGS is
passed only to the compiler, so flags that are only appropriate for that step
(-I and -D flags, for example), should be in _CPPFLAGS instead of _CFLAGS.
Every gnucash-2.2.3 Makefile.am that passes -I flags gets it wrong, placing
them in _CFLAGS. It's not a functional bug (the linker ignores -I flags), but a
ton of superfluous flags makes the build output pretty verbose and hard to
debug when things do go wrong.
To make matters more confusing as a developer, the FOO_CFLAGS variable set by
PKG_CHECK_MODULES(FOO) is actually for _CPPFLAGS in the Makefile.am
('pkg-config --cflags' returns the -I flags).
A related -I bug (one that *is* functionally broken) is that sometimes a local
(build dir) -I flag is passed after a global (installed dependent library) one.
If my system happens to have a header installed from some unrelated thing,
compiler will find *that* one instead of the expected one in the source
directory. Should always pass all local -I before any global ones.
Patch by andi5 plus one manual addition in src/gnome-utils/Makefile.am
git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@17655 57a11ea4-9604-0410-9ed3-97b8803252fd
