[AIX] Include symbol alias in extract_symbols.py

[jsji]

Summary

nm does not show size for aliased symbols,
we should still extract them if they are external.

[hubert.reinterpretcast]

LGTM; thanks!

llvm/utils/extract_symbols.py

if sys.platform.startswith('aix'):
                                    universal_newlines=True)
     else:
         process = subprocess.Popen(['nm','-P',lib], bufsize=1,
                                    stdout=subprocess.PIPE, stdin=subprocess.PIPE,
                                    universal_newlines=True)
     process.stdin.close()
     for line in process.stdout:
         # Look for external symbols that are defined in some section
-        match = re.match("^(\S+)\s+[BDGRSTVW]\s+\S+\s+\S+$", line)
+        # The POSIX format is:
+        #   name   type   value   size
+        # The -P flag displays the size field for symbols only when applicable,
+        # so the last field is optional. There's no space after the value field,
+        # but \s+ match newline also, so \s+\S* will match the optional size field.
+        match = re.match("^(\S+)\s+[BDGRSTVW]\s+\S+\s+\S*$", line)
         if match:
             yield match.group(1)
     process.wait()
 
 def readobj_get_symbols(lib):
     process = subprocess.Popen(['llvm-readobj','-symbols',lib], bufsize=1,
                                stdout=subprocess.PIPE, stdin=subprocess.PIPE,
                                universal_newlines=True)