[extract_symbols.py] Fix line-splitting of tool output.

[simon_tatham]

Summary

Two functions in the is_32bit_windows family were retrieving the
output of a tool via subprocess.check_output, and then iterating
over it using for line in output. But in Python, that gets you the
output one character at a time, not a line at a time. So the
regexes that looked for a platform name were never matching.

(This is a mistake that Python makes uniquely easy, because iterating
over a file and over a string have different default behaviour, and
because the element type of a string is still a string so you don't
even get a type mismatch error to warn you about it!)

[michaelplatings]

LGTM.

Tangent: extract_symbols.py is sorely in need of automated tests.

llvm/utils/extract_symbols.py

for line in process.stdout:
             break
     process.stdout.close()
     process.wait()
     return retval
 
 def objdump_is_32bit_windows(lib):
     output = subprocess.check_output(['objdump','-f',lib],
                                      universal_newlines=True)
-    for line in output:
+    for line in output.splitlines():
         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-header',lib],
                                      universal_newlines=True)
-    for line in output:
+    for line in output.splitlines():
         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,
 # so just assume false.
 def aix_is_32bit_windows(lib):