SDL: Under MSVC, build project-sources in parallel.

SDL Commits
1 
From 3ea82eaaff84efa668a0b080f43315690fa518f1 Mon Sep 17 00:00:00 2001
From: ulatekh <[EMAIL REDACTED]>
Date: Tue, 4 Jan 2022 15:46:04 -0700
Subject: [PATCH] Under MSVC, build project-sources in parallel.

---
 CMakeLists.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 76cc3c51653..afbddce05b8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,6 +23,11 @@ if(WINDOWS_STORE)
   target_compile_options(sdl-build-options INTERFACE "-ZW")
 endif()
 
+# Build in parallel under Visual Studio. Not enabled by default.
+if(MSVC)
+  target_compile_options(sdl-build-options INTERFACE "/MP")
+endif(MSVC)
+
 
 # !!! FIXME: this should probably do "MACOSX_RPATH ON" as a target property
 # !!! FIXME:  for the SDL2 shared library (so you get an