sdl12-compat: FIXME removal: Added a conditional `#warning` for the unimplemented path.

SDL Commits
1 
From af3155aa7569c846b79df6929a9a2326ae3572fc Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Thu, 1 Sep 2022 00:08:13 -0400
Subject: [PATCH] FIXME removal: Added a conditional `#warning` for the
 unimplemented path.

---
 src/SDL12_compat.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 657de402..7dcc6ba1 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -1235,7 +1235,8 @@ static void OS_GetExeName(char *buf, const unsigned maxpath) {
     buf[0] = '\0';
     DosQueryModuleName(pib->pib_hmte, maxpath, buf);
 }
-#else /* FIXME */
+#else
+#warning Please implement this for your platform.
 static void OS_GetExeName(char *buf, const unsigned maxpath) {
     buf[0] = '\0';
     (void)maxpath;