cmake: Only prevent MSVC codegen using the CRT if SDL_LIBC=OFF

CMakeLists.txt

@@ -237,12 +237,14 @@ if(MSVC)
     endforeach()
   endif()
 
-  # Make sure /RTC1 is disabled, otherwise it will use functions from the CRT
-  foreach(flag_var
-      CMAKE_C_FLAGS CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_RELEASE
-      CMAKE_C_FLAGS_MINSIZEREL CMAKE_C_FLAGS_RELWITHDEBINFO)
-    string(REGEX REPLACE "/RTC(su|[1su])" "" ${flag_var} "${${flag_var}}")
-  endforeach(flag_var)
+  if(NOT SDL_LIBC)
+    # Make sure /RTC1 is disabled, otherwise it will use functions from the CRT
+    foreach(flag_var
+        CMAKE_C_FLAGS CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_RELEASE
+        CMAKE_C_FLAGS_MINSIZEREL CMAKE_C_FLAGS_RELWITHDEBINFO)
+      string(REGEX REPLACE "/RTC(su|[1su])" "" ${flag_var} "${${flag_var}}")
+    endforeach(flag_var)
+  endif()
 endif()
 
 # Those are used for pkg-config and friends, so that the SDL2.pc, sdl2-config,
@@ -1469,7 +1471,7 @@ elseif(WINDOWS)
     list(APPEND SOURCE_FILES ${WINRT_SOURCE_FILES})
   endif()
 
-  if(MSVC)
+  if(MSVC AND NOT SDL_LIBC)
     # Prevent codegen that would use the VC runtime libraries.
     set_property(DIRECTORY . APPEND PROPERTY COMPILE_OPTIONS "/GS-")
     if(NOT ARCH_64)