Cleanup: Use Bit('build_ARCH') instead of Bit('target_ARCH')

tests/gdb/nacl.scons

Index: tests/gdb/nacl.scons
diff --git a/tests/gdb/nacl.scons b/tests/gdb/nacl.scons
index 9e7437dbb1322a3d9e6a639426aa55f72e241f0b..ade00cffca5c0632db631d5f3b1664a7eda445a3 100644
--- a/tests/gdb/nacl.scons
+++ b/tests/gdb/nacl.scons
@@ -13,7 +13,7 @@ if 'TRUSTED_ENV' not in env:
 if env.UnderWindowsCoverage():
   Return()
 
-if env.Bit('build_arm') or env.Bit('target_mips32'):
+if env.Bit('build_arm') or env.Bit('build_mips32'):
   if env.UsingEmulator():
     # nacl-gdb is built with ARM support but not MIPS support.
     if env.Bit('build_mips32'):