build: Don't bail on OSError in git_sha1_gen.py

When building sandboxed, we may encounter additional errors. Ignore the errors,
as we are in a constrained environment.

This can be observed when building latest git with OBS.

Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

bin/git_sha1_gen.py

@@ -16,5 +16,8 @@ try:
 except subprocess.CalledProcessError as e:
     # don't print anything if git fails
     pass
+except OSError as eos:
+    # don't fail on inaccessible files when sandboxed
+    pass
 else:
     sys.stdout.write('#define MESA_GIT_SHA1 "git-%s"\n' % git_sha1.rstrip())