[libc++] Fix codesigning in run.py

[ldionne]

Summary

Without this patch, we'd always try to codesign the first argument in
the command line, which in some cases is not something we can codesign
(e.g. bash for some .sh.cpp tests).

[mstorsjo]

LGTM, but I guess it'd be good to mention somewhere in the commit message that this isn't a new "hack" (and I'm not sure I'd agree to even label it as a hack) but this just is a straight copy of the same code in ssh.py.

[ldionne]

In D99726#2663802, @mstorsjo wrote:

LGTM, but I guess it'd be good to mention somewhere in the commit message that this isn't a new "hack" (and I'm not sure I'd agree to even label it as a hack) but this just is a straight copy of the same code in ssh.py.

Will do, thanks.

libcxx/utils/run.py

def main():
     parser = argparse.ArgumentParser()
     parser.add_argument('--execdir', type=str, required=True)
     parser.add_argument('--codesign_identity', type=str, required=False, default=None)
     parser.add_argument('--env', type=str, nargs='*', required=False, default=dict())
     parser.add_argument("command", nargs=argparse.ONE_OR_MORE)
     args = parser.parse_args()
     commandLine = args.command
 
-    # Do any necessary codesigning.
+    # HACK:
+    # If an argument is a file that ends in `.tmp.exe`, assume it is the name
+    # of an executable generated by a test file. We call these test-executables
+    # below. This allows us to do custom processing like codesigning test-executables.
+    # It's also possible for there to be no such executable, for example in the case
+    # of a .sh.cpp test.
+    isTestExe = lambda exe: exe.endswith('.tmp.exe') and os.path.exists(exe)
+
+    # Do any necessary codesigning of test-executables found in the command line.
     if args.codesign_identity:
-        exe = commandLine[0]
-        rc = subprocess.call(['xcrun', 'codesign', '-f', '-s', args.codesign_identity, exe], env={})
-        if rc != 0:
-            sys.stderr.write('Failed to codesign: ' + exe)
-            return rc
+        for exe in filter(isTestExe, commandLine):
+            subprocess.check_call(['xcrun', 'codesign', '-f', '-s', args.codesign_identity, exe], env={})
 
     # Extract environment variables into a dictionary
     env = {k : v  for (k, v) in map(lambda s: s.split('=', 1), args.env)}
     if platform.system() == 'Windows':
         # Pass some extra variables through on Windows:
         # COMSPEC is needed for running subprocesses via std::system().
         if 'COMSPEC' in os.environ:
             env['COMSPEC'] = os.environ.get('COMSPEC')