SDL: Fix tests configuration and building when only GLVND full OpenGL implementation is present.

From e6b87005c1da22a0d354619eebca53c6e2639cdd Mon Sep 17 00:00:00 2001
From: Vanfanel <[EMAIL REDACTED]>
Date: Wed, 17 Mar 2021 20:10:31 +0100
Subject: [PATCH] Fix tests configuration and building when only GLVND full
 OpenGL implementation is present.

---
 test/configure.ac | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/configure.ac b/test/configure.ac
index a22e1a98e..7aad98fe4 100644
--- a/test/configure.ac
+++ b/test/configure.ac
@@ -80,7 +80,15 @@ case "$host" in
         ISUNIX="true"
         EXE=""
         MATHLIB="-lm"
+        dnl Use the new libOpenGL if present.
+        have_glvnd=no
+        AC_CHECK_LIB(OpenGL, glBegin,
+        [   
+        dnl have_glvnd=yes
+        SYS_GL_LIBS="-lOpenGL"
+        ],[ 
         SYS_GL_LIBS="-lGL"
+        ])  
         ;;
 esac
 AC_SUBST(EXE)