ref_gl: add an option to disable ref_gl building

ref_gl/wscript

@@ -18,6 +18,9 @@ def options(opt):
 
 	grp.add_option('--enable-gles2', action='store_true', dest='GLWES',
 	    help = 'enable gles2 renderer by linking gl-wes-v2 statically(put source to ref_gl directory)')
+	
+	grp.add_option('--disable-gl', action='store_false', dest='GL', default=True,
+		help = 'disable building OpenGL renderer(default: False)')
 
 	# stub
 	return
@@ -66,16 +69,17 @@ def build(bld):
 		if glstatic: return ['XASH_GL_STATIC']
 		else: return []
 
-	bld.shlib(
-		source   = source,
-		target   = 'ref_gl',
-		features = 'c',
-		includes = includes,
-		use      = libs + link_gl(bld.env.GL_STATIC),
-		defines  = static_gl(bld.env.GL_STATIC),
-		install_path = bld.env.LIBDIR,
-		subsystem = bld.env.MSVC_SUBSYSTEM
-	)
+	if bld.env.GL:
+		bld.shlib(
+			source   = source,
+			target   = 'ref_gl',
+			features = 'c',
+			includes = includes,
+			use      = libs + link_gl(bld.env.GL_STATIC),
+			defines  = static_gl(bld.env.GL_STATIC),
+			install_path = bld.env.LIBDIR,
+			subsystem = bld.env.MSVC_SUBSYSTEM
+		)
 
 	if bld.env.NANOGL:
 		bld.add_subproject('nanogl')