Add support for ccache

For CMake builds, it now checks if ccache is available on the system,
and enables it if found.
This isn't a big project, but it still provides a nice speed boost for
rebuilds, especially when switching between release and debug.

The way I have it structured is not optimal, I don't use a build
directory for the different build types, and instead just rebuild the
whole thing from scratch.
Should probably fix it somehow, I'm just so used to how it is now :D

CMakeLists.txt

@@ -62,6 +62,8 @@ message(STATUS "Build type: ${CMAKE_BUILD_TYPE}")
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${c-ray_SOURCE_DIR}/cmake")
 file(GLOB_RECURSE SOURCES src/*.c)
 
+include(set_up_ccache)
+
 include(GetGitRevisionDescription)
 get_git_head_revision(GIT_REFSPEC GIT_SHA1)
 configure_file("${c-ray_SOURCE_DIR}/src/utils/gitsha1.c.in" "${c-ray_BINARY_DIR}/generated/gitsha1.c" @ONLY)

cmake/set_up_ccache.cmake

@@ -0,0 +1,9 @@
+find_program(CCACHE_PROGRAM ccache)
+if (CCACHE_PROGRAM)
+	get_filename_component(compiler_path "${CMAKE_C_COMPILER}" REALPATH)
+	get_filename_component(compiler_name "${compiler_path}" NAME)
+	if (NOT ${compiler_name} MATCHES "ccache")
+		message(STATUS "Enabling ccache")
+		set("CMAKE_C_COMPILER_LAUNCHER" "${CCACHE_PROGRAM}" CACHE FILEPATH "Path to a compiler launcher, usually ccache")
+	endif()
+endif()