cmake: don't use ccache on msys2+ninja

When using msys ccache with a mingw ninja, the compiler fails to
execute.

Don't try to detect ccache when using the Ninja generator on msys2, it
can still be specified through cmake variables.

Do not check for the mingw ccache because it is broken and I will assume
not being used.
Signed-off-by: Rafael Kitover <rkitover@gmail.com>

CMakeLists.txt

@@ -40,12 +40,15 @@ endif()
 set(ASM_DEFAULT OFF)
 
 # use ccache if available, and not already enabled on the command line
-if(NOT CMAKE_CXX_COMPILER_LAUNCHER AND NOT CMAKE_C_COMPILER_LAUNCHER)
+# but not with ninja and msys ccache on msys2
+if(NOT (WIN32 AND (NOT $ENV{MSYSTEM} STREQUAL "") AND CMAKE_GENERATOR STREQUAL Ninja))
+    if(NOT CMAKE_CXX_COMPILER_LAUNCHER AND NOT CMAKE_C_COMPILER_LAUNCHER)
         find_program(CCACHE_FOUND ccache)
         if(CCACHE_FOUND)
             set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
             set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
         endif(CCACHE_FOUND)
+    endif()
 endif()
 
 if(NOT CMAKE_SYSTEM_PROCESSOR)