SDL: src/SDL.c: add managarm support

SDL Commits
1 
From ec5088cb9968b7fb890fa198157ecd48e1ad8e9f Mon Sep 17 00:00:00 2001
From: Alexander Richards <[EMAIL REDACTED]>
Date: Fri, 21 Jul 2023 21:01:37 +0200
Subject: [PATCH] src/SDL.c: add managarm support

---
 src/SDL.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/SDL.c b/src/SDL.c
index 8eb90a30f01e..e0381f9fd445 100644
--- a/src/SDL.c
+++ b/src/SDL.c
@@ -609,6 +609,8 @@ const char *SDL_GetPlatform(void)
     return "Nokia N-Gage";
 #elif defined(__3DS__)
     return "Nintendo 3DS";
+#elif defined(__managarm__)
+    return "Managarm";
 #else
     return "Unknown (see SDL_platform.h)";
 #endif