cmake: Replace /Zi with /Z7 for sccache support

Also allows better parallelization since there's no contention on a PDB
file with compiling.

CMake/FlagsOverride.cmake

@@ -0,0 +1,7 @@
+if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+  foreach(f CMAKE_C_FLAGS_DEBUG CMAKE_CXX_FLAGS_DEBUG CMAKE_C_FLAGS_RELWITHDEBINFO CMAKE_CXX_FLAGS_RELWITHDEBINFO)
+	  if("${${f}}" MATCHES "/Zi")
+		  string(REGEX REPLACE "/Zi" "/Z7" "${f}" "${${f}}")
+		endif()
+	endforeach()
+endif()

CMakeLists.txt

@@ -10,6 +10,8 @@ set(CMAKE_OSX_ARCHITECTURES "x86_64")
 # handle configuration options
 set(CMAKE_OSX_DEPLOYMENT_TARGET "10.12.0" CACHE STRING "")
 
+set(CMAKE_USER_MAKE_RULES_OVERRIDE "CMake/FlagsOverride.cmake")
+
 project(dolphin-emu)
 
 # Name of the Dolphin distributor. If you redistribute Dolphin builds (forks,