sdl12-compat: cmake: check immintrin.h and set -DSDL_DISABLE_IMMINTRIN_H if necessary

SDL Commits
1 
From 83db02e68da290861cc1ea418f9037f9886f8d9b Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Fri, 9 Jul 2021 11:55:10 +0300
Subject: [PATCH] cmake: check immintrin.h and set -DSDL_DISABLE_IMMINTRIN_H if
 necessary

just in case. fixes build using older gcc. (yes, I'm being overzealous.)
---
 CMakeLists.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7dc89f5..7a5db29 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -39,6 +39,7 @@ set(SDL12COMPAT_SRCS
 add_library(SDL SHARED ${SDL12COMPAT_SRCS})
 
 include(CheckCSourceCompiles)
+include(CheckIncludeFile)
 include(CheckCCompilerFlag)
 
 include(GNUInstallDirs)
@@ -57,6 +58,11 @@ if (CMAKE_C_COMPILER_ID MATCHES "Clang|GNU")
     set(EXTRA_CFLAGS "${EXTRA_CFLAGS} -Werror=declaration-after-statement")
   endif()
 endif()
+# just in case:
+check_include_file("immintrin.h" HAVE_IMMINTRIN_H)
+if(NOT HAVE_IMMINTRIN_H)
+  set(EXTRA_CFLAGS "${EXTRA_CFLAGS} -DSDL_DISABLE_IMMINTRIN_H")
+endif()
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${EXTRA_CFLAGS}")
 string(STRIP "${CMAKE_C_FLAGS}" CMAKE_C_FLAGS)