gcc: support without command line tools (#11040)

var/spack/repos/builtin/packages/gcc/package.py

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 from spack import *
-from spack.operating_systems.mac_os import macos_version
+from spack.operating_systems.mac_os import macos_version, macos_sdk_path
 from llnl.util import tty
 
 import glob
@@ -315,6 +315,12 @@ def configure_args(self):
                             '--disable-bootstrap',
                             '--disable-multilib'])
 
+        if sys.platform == 'darwin':
+            options.extend([
+                '--with-native-system-header-dir=/usr/include',
+                '--with-sysroot={0}'.format(macos_sdk_path())
+            ])
+
         return options
 
     # run configure/make/make(install) for the nvptx-none target