cmake: Enable full optimizations for RelWithDebInfo MSVC builds

Adds compiler flag:
/Ob2 (automatic inline expansion)

And linker flags:
/OPT:ICF (identical COMDAT folding)

Ref: https://gitlab.kitware.com/cmake/cmake/-/issues/20812

CMakeLists.txt

@@ -175,6 +175,10 @@ if(MSVC)
 	set(CMAKE_C_FLAGS_DEBUG "/DDEBUG=1 /D_DEBUG=1 ${CMAKE_C_FLAGS_DEBUG}")
 	set(CMAKE_CXX_FLAGS_DEBUG "/DDEBUG=1 /D_DEBUG=1 ${CMAKE_C_FLAGS_DEBUG}")
 
+	# https://gitlab.kitware.com/cmake/cmake/-/issues/20812
+	set(CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO} /Ob2")
+	set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} /Ob2")
+
 	if(NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
 		set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /SAFESEH:NO")
 		set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} /SAFESEH:NO")
@@ -184,7 +188,7 @@ if(MSVC)
 	foreach(t EXE SHARED MODULE)
 		set(CMAKE_${t}_LINKER_FLAGS "${CMAKE_${t}_LINKER_FLAGS} /OPT:REF")
 		set(CMAKE_${t}_LINKER_FLAGS_DEBUG "${CMAKE_${t}_LINKER_FLAGS_DEBUG} /INCREMENTAL:NO")
-		set(CMAKE_${t}_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_${t}_LINKER_FLAGS_RELWITHDEBINFO} /INCREMENTAL:NO")
+		set(CMAKE_${t}_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_${t}_LINKER_FLAGS_RELWITHDEBINFO} /INCREMENTAL:NO /OPT:ICF")
 	endforeach()
 else()
 	if(MINGW)