Add llvm-mc to the set of commands lit knows about.

tests_lit/lit.cfg

 # Taken from utils/lit/tests in the LLVM tree and hacked together to support
 # our tests.
 
 # -*- Python -*-
 
 import os
 import re
 import sys
 
 import lit.formats
@@ skipping 24 matching lines @@
 # Finding Subzero tools
 llvm2icetool = os.path.join(bin_root, 'llvm2ice')
 config.substitutions.append(
   ('%llvm2iceinsts', ' '.join([os.path.join(bin_root, 'llvm2iceinsts.py'),
                                '--llvm2ice', llvm2icetool,
                                '--llvm-bin-path', llvmbinpath
                              ])))
 config.substitutions.append(('%llvm2ice', llvm2icetool))
 config.substitutions.append(('%szdiff', os.path.join(bin_root, 'szdiff.py')))
 
-llvmbintools = [r"\bFileCheck\b", r"\bnot\b"]
+llvmbintools = [r"\bFileCheck\b", r"\bllvm-mc\b", r"\bnot\b"]
 
 for tool in llvmbintools:
   # The re.sub() line is adapted from one of LLVM's lit.cfg files.
   # Extract the tool name from the pattern.  This relies on the tool
   # name being surrounded by \b word match operators.  If the
   # pattern starts with "| ", include it in the string to be
   # substituted.
   substitution = re.sub(r"^(\\)?((\| )?)\W+b([0-9A-Za-z-_]+)\\b\W*$",
                         r"\2" + llvmbinpath + "/" + r"\4",
                         tool)
   config.substitutions.append((tool, substitution))
 
 # Add a feature to detect the Python version.
 config.available_features.add("python%d.%d" % (sys.version_info[0],
                                                sys.version_info[1]))
 
 # Debugging output
 def dbg(s):
   print '[DBG] %s' % s
 
 dbg('bin_root = %s' % bin_root)
 dbg('llvmbinpath = %s' % llvmbinpath)