Add nacl-clang testing to SCons

SConstruct

Index: SConstruct
diff --git a/SConstruct b/SConstruct
index 1661234a75e88514aebf1029af1510114bbf969b..a27fab893441debd9e1359a37aa92e88788a18bd 100755
--- a/SConstruct
+++ b/SConstruct
@@ -261,6 +261,9 @@ def SetUpArgumentBits(env):
   BitFromArgument(env, 'bitcode', default=False,
     desc='We are building bitcode')
 
+  BitFromArgument(env, 'nacl_clang', default=False,
+    desc='Use native nacl-clang compiler')
+
   BitFromArgument(env, 'translate_fast', default=False,
     desc='When using pnacl TC (bitcode=1) use accelerated translation step')
 
@@ -1240,7 +1243,8 @@ def GetToolchainDir(env, platform_build_dir=None, toolchain_name=None,
   if toolchain_name is None:
     # Fill in default arguments based on environment.
     if is_pnacl is None:
-      is_pnacl = env.Bit('bitcode')
+      # For the purposes of finding the toolchain dir, nacl_clang is PNaCl.
+      is_pnacl = env.Bit('bitcode') or env.Bit('nacl_clang')
       if lib_name is None:
         if is_pnacl or not env.Bit('nacl_glibc'):
           lib_name = 'newlib'
@@ -3162,6 +3166,11 @@ if nacl_env.Bit('bitcode'):
   # http://code.google.com/p/nativeclient/issues/detail?id=2861
   nacl_env.Append(CCFLAGS=['-Wno-unused-private-field'])
 
+if nacl_env.Bit('nacl_clang'):
+  nacl_env.Append(CCFLAGS=['-Wno-format-security'])
+  # third_party/valgrind/nacl_valgrind.h uses asm instead of __asm__
+  nacl_env.Append(CCFLAGS=['-Wno-language-extension-token'])
+
 # We use a special environment for building the IRT image because it must
 # always use the newlib toolchain, regardless of --nacl_glibc.  We clone
 # it from nacl_env here, before too much other cruft has been added.
@@ -3190,6 +3199,7 @@ target_variant_map = [
     ('nacl_glibc', 'glibc'),
     ('pnacl_generate_pexe', 'pexe'),
     ('nonsfi_nacl', 'nonsfi'),
+    ('nacl_clang', 'clang'),
     ]
 for variant_bit, variant_suffix in target_variant_map:
   if nacl_env.Bit(variant_bit):
@@ -3659,6 +3669,11 @@ def AddImplicitLibs(env):
       # TODO(mcgrathr): multilib nonsense defeats -B!  figure out a better way.
       if GetTargetPlatform() == 'x86-32':
         implicit_libs.append(os.path.join('32', 'crt1.o'))
+    # libc++ depends on libpthread, and because PPAPI applications always need
+    # threads anyway, nacl-clang just includes -lpthread unconditionally.
+    if ((env.Bit('nacl_clang') or env.Bit('bitcode')) and
+        env['NACL_BUILD_FAMILY'] != 'UNTRUSTED_IRT'):
+      implicit_libs += ['libpthread.a']
 
   if implicit_libs != []:
     env['IMPLICIT_LIBS'] = [env.File(os.path.join('${LIB_DIR}', file))