MAINT: git security shim for 1.9.x (#16329)

replicated gh-16139 on the latest maintenance branch
because the `master` branch of the wheels repo will
encounter the issues described in that PR (for example, see:
MacPython/scipy-wheels#166 which
has Travis and Azure failures caused by those same
versioning issues)

[ci skip]

tools/version_utils.py

@@ -81,7 +81,13 @@ def _minimal_ext_cmd(cmd):
         return out
 
     try:
-        out = _minimal_ext_cmd(['git', 'rev-parse', 'HEAD'])
+        git_dir = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+        git_dir = os.path.join(git_dir, ".git")
+        out = _minimal_ext_cmd(['git',
+                                '--git-dir',
+                                git_dir,
+                                'rev-parse',
+                                'HEAD'])
         GIT_REVISION = out.strip().decode('ascii')[:7]
 
         # We need a version number that's regularly incrementing for newer commits,