Update Clang for rebase to r212749.

This also fixes a small issue with arm_neon.h not being generated always.

Includes a cherry-pick of:
r213450 - fixes mac-specific header issue
r213126 - removes a default -Bsymbolic on Android

Change-Id: I2a790a0f5d3b2aab11de596fc3a74e7cbc99081d
diff --git a/test/lit.cfg b/test/lit.cfg
index 5c2b187..11e8e0b 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -471,18 +471,4 @@
 if use_gmalloc:
      config.environment.update({'DYLD_INSERT_LIBRARIES' : gmalloc_path_str})
 
-# On Darwin, support relocatable SDKs by providing Clang with a
-# default system root path.
-if 'darwin' in config.target_triple:
-    try:
-        cmd = subprocess.Popen(['xcrun', '--show-sdk-path'],
-                               stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-        out, err = cmd.communicate()
-        out = out.strip()
-        res = cmd.wait()
-    except OSError:
-        res = -1
-    if res == 0 and out:
-        sdk_path = out
-        lit_config.note('using SDKROOT: %r' % sdk_path)
-        config.environment['SDKROOT'] = sdk_path
+lit.util.usePlatformSdkOnDarwin(config, lit_config)