Emscripten: Added missing define. (#3498)

src/renderer_gl.h

@@ -445,6 +445,10 @@ typedef uint64_t GLuint64;
 #	define GL_COMPRESSED_RGBA8_ETC2_EAC 0x9278
 #endif // GL_COMPRESSED_RGBA8_ETC2_EAC
 
+#ifndef GL_COMPRESSED_SRGB8_ALPHA8_ETC2_EAC
+#	define GL_COMPRESSED_SRGB8_ALPHA8_ETC2_EAC 0x9279
+#endif // GL_COMPRESSED_SRGB8_ALPHA8_ETC2_EAC
+
 #ifndef GL_COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2
 #	define GL_COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2 0x9276
 #endif // GL_COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2