CMake: Use improved optimization flags on MSVC

While not having a noticeable effect on CPU-bound applications, this
change gives an about 30-50% increase in performance for games using
the GPU.

CMakeLists.txt

@@ -11,6 +11,25 @@ else()
     add_definitions(/D_CRT_SECURE_NO_WARNINGS)
     # set up output paths for executable binaries (.exe-files, and .dll-files on DLL-capable platforms)
     set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
+
+    # Tweak optimization settings
+    # As far as I can tell, there's no way to override the CMake defaults while leaving user
+    # changes intact, so we'll just clobber everything and say sorry.
+    message(STATUS "Cache compiler flags ignored, please edit CMakeFiles.txt to change the flags.")
+    # /MD - Multi-threaded runtime
+    # /Ox - Full optimization
+    # /Oi - Use intrinsic functions
+    # /Oy- - Don't omit frame pointer
+    # /GR- - Disable RTTI
+    # /GS- - No stack buffer overflow checks
+    # /EHsc - C++-only exception handling semantics
+    set(optimization_flags "/MD /Ox /Oi /Oy- /DNDEBUG /GR- /GS- /EHsc")
+    # /Zi - Output debugging information
+    # /Zo - enahnced debug info for optimized builds
+    set(CMAKE_C_FLAGS_RELEASE   "${optimization_flags} /Zi" CACHE STRING "" FORCE)
+    set(CMAKE_CXX_FLAGS_RELEASE "${optimization_flags} /Zi" CACHE STRING "" FORCE)
+    set(CMAKE_C_FLAGS_RELWITHDEBINFO   "${optimization_flags} /Zi /Zo" CACHE STRING "" FORCE)
+    set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${optimization_flags} /Zi /Zo" CACHE STRING "" FORCE)
 endif()
 add_definitions(-DSINGLETHREADED)