The "cmakexbuild" wrapper is not needed for Xcode 4 and above, and the
path to it may change when CMake moves. Avoid storing a specific path
to a build program in CMakeCache.txt and instead compute the value for
CMAKE_MAKE_PROGRAM on demand. However, if a user does set the value
explicitly then honor it.
This does for Xcode what commit v3.0.0-rc1~260^2~4 (VS: Switch to
internal CMAKE_MAKE_PROGRAM lookup by generators, 2013-11-15) did for
Visual Studio generators.
Since commit 5f5c92b9 (VS: Add internal APIs to find MSBuild,
devenv/VCExpress, and msdev, 2013-11-13) the VS generators have
known how to lookup the locations of their build tools directly.
Expose this information to CMake language code by defining new
variables to hold the paths to these tools.
Historically these were both added for the Makefile and Visual Studio
generators, respectively. Later the VS generators started using the
CMAKE_MAKE_PROGRAM cache entry to find the IDE build tool, and the
CMAKE_BUILD_TOOL was simply set as an alias.
Fix the documentation to explain that CMAKE_MAKE_PROGRAM is the modern
variable and that CMAKE_BUILD_TOOL is the compatibility alias, not the
other way around. Replace uses of CMAKE_BUILD_TOOL with
CMAKE_MAKE_PROGRAM in CMake-provided modules. Nothing needs to lookup
CMAKE_BUILD_TOOL in the cache, so simply set it as a normal variable.