[extract_symbols.py] Fix llvm-readobj options.

[simon_tatham]

Summary

As of D105532, a couple of llvm-readobj options have slightly changed
their spellings. '-file-headers' has become '--file-header', and
'-symbols' has become '--symbols'. A modern llvm-readobj will respond
to those single-dash spellings by trying to parse them as combinations
of single-letter options, so that you get "unknown argument '-f'" for
-file-headers, and "unknown argument '-y'" for the second letter of
-symbols.

extract_symbols.py was still invoking llvm-readobj with those old
single-dash spellings. Changed them to the newly canonical ones, which
as far as I can tell still work on llvm-readobj from before the
change.

[MaskRay]

Looks great!

llvm/utils/extract_symbols.py

for line in process.stdout:
         # 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,
+    process = subprocess.Popen(['llvm-readobj','--symbols',lib], bufsize=1,
                                stdout=subprocess.PIPE, stdin=subprocess.PIPE,
                                universal_newlines=True)
     process.stdin.close()
     for line in process.stdout:
         # When looking through the output of llvm-readobj we expect to see Name,
         # Section, then StorageClass, so record Name and Section when we see
         # them and decide if this is a defined external symbol when we see
         # StorageClass.
output = subprocess.check_output(['objdump','-f',lib],
                                      universal_newlines=True)
     for line in output:
         match = re.match('.+file format (\S+)', line)
         if match:
             return (match.group(1) == 'pe-i386')
     return False
 
 def readobj_is_32bit_windows(lib):
-    output = subprocess.check_output(['llvm-readobj','-file-headers',lib],
+    output = subprocess.check_output(['llvm-readobj','--file-header',lib],
                                      universal_newlines=True)
     for line in output:
         match = re.match('Format: (\S+)', line)
         if match:
             return (match.group(1) == 'COFF-i386')
     return False
 
 # On AIX, there isn't an easy way to detect 32-bit windows objects with the system toolchain,