Fixed issue #1927.

src/renderer_gl.h

@@ -556,6 +556,14 @@ typedef uint64_t GLuint64;
 #	define GL_COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB 0x8E8F
 #endif // GL_COMPRESSED_RGB_BPTC_UNSIGNED_FLOAT_ARB
 
+#ifndef GL_SRGB_EXT
+#	define GL_SRGB_EXT 0x8C40
+#endif // GL_SRGB_EXT
+
+#ifndef GL_SRGB_ALPHA_EXT
+#	define GL_SRGB_ALPHA_EXT 0x8C42
+#endif // GL_SRGB_ALPHA_EXT
+
 #ifndef GL_SRGB8_ALPHA8
 #	define GL_SRGB8_ALPHA8 0x8C43
 #endif // GL_SRGB8_ALPHA8