Revert "SCons: Add CPPEXTPATH for external includes"

drivers/gl_context/SCsub

@@ -13,7 +13,12 @@ if env["platform"] in ["macos", "windows", "linuxbsd"]:
 
     thirdparty_sources = [thirdparty_dir + file for file in thirdparty_sources]
 
-    env.Prepend(CPPEXTPATH=[thirdparty_dir])
+    # Treat glad headers as system headers to avoid raising warnings. Not supported on MSVC.
+    if not env.msvc:
+        env.Append(CPPFLAGS=["-isystem", Dir(thirdparty_dir).path])
+    else:
+        env.Prepend(CPPPATH=[thirdparty_dir])
+
     env.Append(CPPDEFINES=["GLAD_ENABLED"])
     env.Append(CPPDEFINES=["EGL_ENABLED"])