SDL: SDL_kmsdrmvideo.c: define EGL_PLATFORM_GBM_MESA if it's missing.

SDL Commits
1 
From 5262b52ddd83b88544ebff747cf33e9a295cfc0a Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Thu, 25 Mar 2021 23:56:56 +0300
Subject: [PATCH] SDL_kmsdrmvideo.c: define EGL_PLATFORM_GBM_MESA if it's
 missing.

Fixes:		https://github.com/libsdl-org/SDL/issues/4232
---
 src/video/kmsdrm/SDL_kmsdrmvideo.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/video/kmsdrm/SDL_kmsdrmvideo.c b/src/video/kmsdrm/SDL_kmsdrmvideo.c
index c2c5ee0e1..0d3a6c267 100644
--- a/src/video/kmsdrm/SDL_kmsdrmvideo.c
+++ b/src/video/kmsdrm/SDL_kmsdrmvideo.c
@@ -64,6 +64,10 @@
 #define KMSDRM_DRI_CARDPATHFMT "/dev/dri/card%d"
 #endif
 
+#ifndef EGL_PLATFORM_GBM_MESA
+#define EGL_PLATFORM_GBM_MESA 0x31D7
+#endif
+
 static int
 check_modestting(int devindex)
 {
@@ -1457,7 +1461,7 @@ KMSDRM_GetWindowWMInfo(_THIS, SDL_Window * window, struct SDL_SysWMinfo *info)
      const Uint32 version = SDL_VERSIONNUM((Uint32)info->version.major,
                                            (Uint32)info->version.minor,
                                            (Uint32)info->version.patch);
- 
+
      if (version < SDL_VERSIONNUM(2, 0, 15)) {
          SDL_SetError("Version must be 2.0.15 or newer");
          return SDL_FALSE;
@@ -1467,7 +1471,7 @@ KMSDRM_GetWindowWMInfo(_THIS, SDL_Window * window, struct SDL_SysWMinfo *info)
      info->info.kmsdrm.dev_index = viddata->devindex;
      info->info.kmsdrm.drm_fd = viddata->drm_fd;
      info->info.kmsdrm.gbm_dev = viddata->gbm_dev;
- 
+
      return SDL_TRUE;
 }