[Build][Bugfix] Use CMAKE_ prefix for <LANG>_COMPILER_LAUNCHER (#13697)

Previously, when using `set(USE_CCACHE AUTO)`, the cmake config would
set variables `CXX_COMPILER_LAUNCHER` and `C_COMPILER_LAUNCHER`.
While there are the target-specific properties named
[`<LANG>_COMPILER_LAUNCHER`](https://cmake.org/cmake/help/latest/prop_tgt/LANG_COMPILER_LAUNCHER.html),
cmake doesn't check for their use as global variables.

This commit updates the build file to instead set the
[`CMAKE_<LANG>_COMPILER_LAUNCHER`](https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER_LAUNCHER.html)
variables, which are used as the default for the
`<LANG>_COMPILER_LAUNCHER` property.

Author: Lunderberg

cmake/utils/CCache.cmake

@@ -16,11 +16,11 @@
 # under the License.
 
 if(USE_CCACHE) # True for AUTO, ON, /path/to/ccache
-  if(DEFINED CXX_COMPILER_LAUNCHER OR DEFINED C_COMPILER_LAUNCHER)
+  if(DEFINED CMAKE_CXX_COMPILER_LAUNCHER OR DEFINED CMAKE_C_COMPILER_LAUNCHER)
     if("${USE_CCACHE}" STREQUAL "AUTO")
-      message(STATUS "CXX_COMPILER_LAUNCHER or C_COMPILER_LAUNCHER already defined, not using ccache")
+      message(STATUS "CMAKE_CXX_COMPILER_LAUNCHER or CMAKE_C_COMPILER_LAUNCHER already defined, not using ccache")
     elseif("${USE_CCACHE}" MATCHES ${IS_TRUE_PATTERN})
-      message(FATAL_ERROR "CXX_COMPILER_LAUNCHER or C_COMPILER_LAUNCHER is already defined, refusing to override with ccache. Either unset or disable ccache.")
+      message(FATAL_ERROR "CMAKE_CXX_COMPILER_LAUNCHER or CMAKE_C_COMPILER_LAUNCHER is already defined, refusing to override with ccache. Either unset or disable ccache.")
     endif()
   else()
     if("${USE_CCACHE}" STREQUAL "AUTO") # Auto mode
@@ -45,8 +45,8 @@ if(USE_CCACHE) # True for AUTO, ON, /path/to/ccache
     endif()
     # Set the flag for ccache
     if(DEFINED PATH_TO_CCACHE)
-      set(CXX_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
-      set(C_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
+      set(CMAKE_CXX_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
+      set(CMAKE_C_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
     endif()
   endif()
 endif(USE_CCACHE)

cmake/utils/Summary.cmake

@@ -42,7 +42,7 @@ macro(print_summary)
     message(STATUS "  C++ compiler ID       : ${CMAKE_CXX_COMPILER_ID}")
     message(STATUS "  C++ compiler version  : ${CMAKE_CXX_COMPILER_VERSION}")
     message(STATUS "  CXX flags             : ${CMAKE_CXX_FLAGS}")
-    message(STATUS "  CXX launcher          : ${CXX_COMPILER_LAUNCHER}")
+    message(STATUS "  CXX launcher          : ${CMAKE_CXX_COMPILER_LAUNCHER}")
     message(STATUS "  Linker flags          : ${CMAKE_SHARED_LINKER_FLAGS}")
     message(STATUS "  Build type            : ${CMAKE_BUILD_TYPE}")
     get_directory_property(READABLE_COMPILE_DEFS DIRECTORY ${PROJECT_SOURCE_DIR} COMPILE_DEFINITIONS)