utils: Tweak clang-parse-diagnostics-file for modules includes

[dexonsmith]

Summary

Diagnostics from modules do not have a main-file listed. Tweak
clang-parse-diagnostics-file to patch this up. Previously, the call
to os.path.basename would crash.

Radar-Id: rdar://problem/59000292

[arphaman]

LGTM. Looks like we don't have tests for this script, it would be nice to add some in the future, but that shouldn't block this.

[dexonsmith]

In D77321#1958052, @arphaman wrote:

LGTM.

0c85c488e2b5be54ce26c9f772e66d48a9290c51

Looks like we don't have tests for this script, it would be nice to add some in the future, but that shouldn't block this.

Yeah, we're missing tests for most of llvm/utils it seems.

llvm/utils/clang-parse-diagnostics-file

 </plist>""" % data
 
     # Get the list of files and diagnostics to report.
     to_report = []
     diags = plistlib.readPlistFromString(data)
     for file_diags in diags:
         file = file_diags.get('main-file')
 
+        # Diagnostics from modules don't have a main-file listed.
+        if not file:
+            file = '<module-includes>'
+
         # Ignore diagnostics for 'conftest.c', which is the file autoconf uses
         # for its tests (which frequently will have warnings).
         if os.path.basename(file) == 'conftest.c':
             continue
 
         # Get the diagnostics for the selected levels.
         selected_diags = [d
                           for d in file_diags.get('diagnostics', ())