[extract_symbols.py] Export unique symbols

[tmatheson]

Summary

As described in a comment on D140637, PluginInlineOrderTest.NoInlineFoo
will fail with:

InlineOrderPlugin.so: undefined symbol: _ZN4llvm13AllAnalysesOnINS_6ModuleEE6SetKeyE

The symbol is unique in libLLVMCore and ends up local in AnalysisTests.
Fix this by exporting all unique symbols found in libraries.

AnalysisTests.symbols change in line count: 12464 -> 12499

llvm/utils/extract_symbols.py

def nm_get_symbols(lib):
     process.stdin.close()
     for line in process.stdout:
         # Look for external symbols that are defined in some section
         # 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*$", line)
+        match = re.match("^(\S+)\s+[BDGRSTuVW]\s+\S+\s+\S*$", line)
         if match:
             yield (match.group(1), True)
         # Look for undefined symbols, which have type U and may or may not
         # (depending on which nm is being used) have value and size.
         match = re.match("^(\S+)\s+U\s+(\S+\s+\S*)?$", line)
         if match:
             yield (match.group(1), False)
     process.wait()