Add detection of OS X relocatable SDK to compiler-rt as a lit.util function

Clang's lit cfg already detects the currently selected SDK via
"xcrun --show-sdk-path". The same thing should be done for compiler-rt tests,
to make them work on recent OS X versions. Instead of duplicating the detection
code, this patch extracts the detection function into a lit.util method.

Patch by Kuba Brecka (kuba.brecka@gmail.com),
reviewed at http://reviews.llvm.org/D4072


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210534 91177308-0d34-0410-b5e6-96231b3b80d8

utils/lit/lit/util.py

@@ -167,3 +167,20 @@ def executeCommand(command, cwd=None, env=None):
         err = str(err)
 
     return out, err, exitCode
+
+def usePlatformSdkOnDarwin(config, lit_config):
+    # 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