scons: added support of default Python installation on MacOS

Recent MacOS versions are distributed with python 2.7.
This version of python is sufficient to compile and run gem5.

This patch allows to use the default python instead of the version provided
by third-party tools (e.g., brew)

The default MacOS LLDB debugger is linked against the default python
installation, which conflicts with Python framework provided by third-party
package systems.

This patch removes the need of gem5 to have multiple python installations
on MacOS, if not explicitly installed.

Change-Id: I98f24804149cb2e04ca432c66d2f57e0296af7b2
Reviewed-on: https://gem5-review.googlesource.com/c/15475
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

SConstruct

@@ -92,6 +92,7 @@ from os import mkdir, environ
 from os.path import abspath, basename, dirname, expanduser, normpath
 from os.path import exists,  isdir, isfile
 from os.path import join as joinpath, split as splitpath
+from re import match
 
 # SCons includes
 import SCons
@@ -710,9 +711,11 @@ if main['USE_PYTHON']:
                                     exception='').strip()
     py_includes = readCommand([python_config, '--includes'],
                               exception='').split()
+    py_includes = filter(lambda s: match(r'.*\/include\/.*',s), py_includes)
     # Strip the -I from the include folders before adding them to the
     # CPPPATH
-    main.Append(CPPPATH=map(lambda inc: inc[2:], py_includes))
+    py_includes = map(lambda s: s[2:] if s.startswith('-I') else s, py_includes)
+    main.Append(CPPPATH=py_includes)
 
     # Read the linker flags and split them into libraries and other link
     # flags. The libraries are added later through the call the CheckLib.