[infra] Workaround Python binary pecularities on Mac OS X

For some reason `python3` binary shipped with Mac OS X
sets LIBRARY_PATH, SDKROOT and CPATH environment variables.

This affects clang if it is spawned in such a modified environment,
because it picks and uses those values.

This CL simply removes these variables from the environment
if they are present.

See also https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4149962

Fixes #52411

[email protected]

Change-Id: Id71ece4c3232c3e9ad19dc07d7546d1012d6330f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/306540
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Slava Egorov <[email protected]>

Author: mraleph

tools/build.py

@@ -251,6 +251,19 @@ def Main():
     env = dict(os.environ)
     env.update(SanitizerEnvironmentVariables())
 
+    # macOS's python sets CPATH, LIBRARY_PATH, SDKROOT implicitly.
+    #
+    # See:
+    #
+    #   * https://openradar.appspot.com/radar?id=5608755232243712
+    #   * https://github.com/dart-lang/sdk/issues/52411
+    #
+    # Remove these environment variables to avoid affecting clang's behaviors.
+    if sys.platform == 'darwin':
+        env.pop('CPATH', None)
+        env.pop('LIBRARY_PATH', None)
+        env.pop('SDKROOT', None)
+
     # Always run GN before building.
     gn_py.RunGnOnConfiguredConfigurations(options)