[MIPS] Fix missing definitions for MIPS arch in build and driver scripts

pnacl/driver/pnacl-driver.py

 #!/usr/bin/python
 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # IMPORTANT NOTE: If you make local mods to this file, you must run:
 #   %  pnacl/build.sh driver
 # in order for them to take effect in the scons build.  This command
 # updates the copy in the toolchain/ tree.
 #
@@ skipping 38 matching lines @@
                           # type set (using -x) unless -E is specified.
   'VERBOSE'     : '0',    # Verbose (-v)
 
   'PTHREAD'     : '0',   # use pthreads?
   'INPUTS'      : '',    # Input files
   'OUTPUT'      : '',    # Output file
   'UNMATCHED'   : '',    # Unrecognized parameters
 
   'BIAS_NONE'   : '',
   'BIAS_ARM'    : '-D__arm__ -D__ARM_ARCH_7A__ -D__ARMEL__',
+  'BIAS_MIPS32' : '-D__MIPS__ -D__mips__ -D__MIPSEL__',
   'BIAS_X8632'  : '-D__i386__ -D__i386 -D__i686 -D__i686__ -D__pentium4__',
   'BIAS_X8664'  : '-D__amd64__ -D__amd64 -D__x86_64__ -D__x86_64 -D__core2__',
   'FRONTEND_TRIPLE' : 'le32-unknown-nacl',
 
   'OPT_LEVEL'   : '',  # Default for most tools is 0, but we need to know
                        # if it's explicitly set or not when the driver
                        # is only used for linking + translating.
   'CC_FLAGS'    : '-O${#OPT_LEVEL ? ${OPT_LEVEL} : 0} ' +
                   '-fno-common ${PTHREAD ? -pthread} ' +
                   '-nostdinc ${BIAS_%BIAS%} ' +
@@ skipping 633 matching lines @@
   -g                    Generate complete debug information.
   -gline-tables-only    Generate debug line-information only
                         (allowing for stack traces).
   -flimit-debug-info    Generate limited debug information.
   -save-temps           Keep intermediate compilation results.
   -v                    Verbose output / show commands.
   -h | --help           Show this help.
   --help-full           Show underlying clang driver's help message
                         (warning: not all options supported).
 """ % (tool)