build: pull iconv detection into its own FindIconv.cmake file

This will provide better control for those who may want to alter which
one gets used.

CMakeLists.txt

@@ -131,6 +131,11 @@ if(LibIntl_FOUND)
   include_directories(SYSTEM ${LibIntl_INCLUDE_DIRS})
 endif()
 
+find_package(Iconv)
+if(Iconv_FOUND)
+  include_directories(SYSTEM ${Iconv_INCLUDE_DIRS})
+endif()
+
 # Determine platform's threading library. Set CMAKE_THREAD_PREFER_PTHREAD
 # explicitly to indicate a strong preference for pthread.
 set(CMAKE_THREAD_PREFER_PTHREAD ON)

cmake/FindIconv.cmake

@@ -0,0 +1,18 @@
+# - Try to find iconv
+# Once done, this will define
+#
+#  Iconv_FOUND        - system has iconv
+#  Iconv_INCLUDE_DIRS - the iconv include directories
+#  Iconv_LIBRARIES    - link these to use iconv
+
+include(LibFindMacros)
+
+find_path(ICONV_INCLUDE_DIR NAMES iconv.h)
+find_library(ICONV_LIBRARY NAMES iconv)
+
+set(Iconv_PROCESS_INCLUDES ICONV_INCLUDE_DIR)
+if(ICONV_LIBRARY)
+  set(Iconv_PROCESS_LIBS ICONV_LIBRARY)
+endif()
+
+libfind_process(Iconv)

config/CMakeLists.txt

@@ -44,12 +44,9 @@ check_function_exists(getpwent HAVE_GETPWENT)
 check_function_exists(getpwnam HAVE_GETPWNAM)
 check_function_exists(getpwuid HAVE_GETPWUID)
 
-check_include_files(iconv.h HAVE_ICONV_H)
-check_library_exists(iconv iconv "" HAVE_ICONV_LIB)
-if(HAVE_ICONV_LIB)
-  set(CMAKE_REQUIRED_LIBRARIES iconv)
+if(Iconv_FOUND)
+  set(HAVE_ICONV 1)
 endif()
-check_function_exists(iconv HAVE_ICONV)
 
 check_function_exists(lstat HAVE_LSTAT)
 if(NOT HAVE_LSTAT)

src/nvim/CMakeLists.txt

@@ -158,8 +158,8 @@ else()
   endif()
 endif()
 
-if(HAVE_ICONV_LIB)
-  list(APPEND NVIM_LINK_LIBRARIES iconv)
+if(Iconv_LIBRARIES)
+  list(APPEND NVIM_LINK_LIBRARIES ${Iconv_LIBRARIES})
 endif()
 
 # Put these last on the link line, since multiple things may depend on them.