SDL: added Watcom i386 inline asm for SDL_Swap64()

From b8d2185277bd80e8ccaa31c4a5a7baa08a2afb23 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 23 Feb 2021 17:37:20 +0300
Subject: [PATCH] added Watcom i386 inline asm for SDL_Swap64()

---
 include/SDL_endian.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/SDL_endian.h b/include/SDL_endian.h
index f9a4fd368..cf2eba91e 100644
--- a/include/SDL_endian.h
+++ b/include/SDL_endian.h
@@ -232,6 +232,14 @@ SDL_Swap64(Uint64 x)
   __asm__("bswapq %0": "=r"(x):"0"(x));
     return x;
 }
+#elif defined(__WATCOMC__) && defined(__386__)
+extern _inline Uint64 SDL_Swap64(Uint64);
+#pragma aux SDL_Swap64 = \
+  "bswap eax"     \
+  "bswap edx"     \
+  "xchg eax,edx"  \
+  parm [eax edx]  \
+  modify [eax edx];
 #elif defined(_MSC_VER)
 #pragma intrinsic(_byteswap_uint64)
 #define SDL_Swap64(x) _byteswap_uint64(x)