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

pnacl/driver/driver_env.py

Index: pnacl/driver/driver_env.py
diff --git a/pnacl/driver/driver_env.py b/pnacl/driver/driver_env.py
index 64d95365148acfb79843f7660b942ab00390221d..1f3020ca4916c0d2a0aeef6e659dfb3d90f319ff 100755
--- a/pnacl/driver/driver_env.py
+++ b/pnacl/driver/driver_env.py
@@ -54,10 +54,11 @@ INITIAL_ENV = {
     '${BASE_TOOLCHAIN}/pnacl_translator/${STANDARD_ARCH}/bin',
 
   # TODO(pdox): Unify this with ARCH.
-  'STANDARD_ARCH'      : '${STANDARD_ARCH_%ARCH%}',
-  'STANDARD_ARCH_X8632': 'i686',
-  'STANDARD_ARCH_X8664': 'x86_64',
-  'STANDARD_ARCH_ARM'  : 'armv7',
+  'STANDARD_ARCH'       : '${STANDARD_ARCH_%ARCH%}',
+  'STANDARD_ARCH_X8632' : 'i686',
+  'STANDARD_ARCH_X8664' : 'x86_64',
+  'STANDARD_ARCH_ARM'   : 'armv7',
+  'STANDARD_ARCH_MIPS32': 'mips32',
 
   'SCONS_OUT'       : '${BASE_NACL}/scons-out',
 
@@ -128,6 +129,7 @@ INITIAL_ENV = {
   'SCONS_STAGING_X8632' : '${SCONS_OUT}/opt-${SCONS_OS}-x86-32/staging',
   'SCONS_STAGING_X8664' : '${SCONS_OUT}/opt-${SCONS_OS}-x86-64/staging',
   'SCONS_STAGING_ARM'   : '${SCONS_OUT}/opt-${SCONS_OS}-arm/staging',
+  'SCONS_STAGING_MIPS32': '${SCONS_OUT}/opt-${SCONS_OS}-mips32/staging',
 
   'SEL_UNIVERSAL_PREFIX': '${USE_EMULATOR ? ${EMULATOR}}',
   'SEL_UNIVERSAL'       : '${SCONS_STAGING}/sel_universal${EXEC_EXT}',
@@ -144,6 +146,8 @@ INITIAL_ENV = {
   # NOTE: this is currently the only dependency on the arm trusted TC
   'EMULATOR_ARM'        :
       '${BASE_NACL}/toolchain/linux_arm-trusted/run_under_qemu_arm',
+  'EMULATOR_MIPS32'     :
+      '${BASE_NACL}/toolchain/linux_mips-trusted/run_under_qemu_mips32',
 
   'SEL_LDR'       : '${SCONS_STAGING}/sel_ldr${EXEC_EXT}',
   'BOOTSTRAP_LDR' : '${SCONS_STAGING}/nacl_helper_bootstrap${EXEC_EXT}',