Use the new lit.util.isMacOSTriple function to determine if a target triple is a macOS target triple.

See 01436117652b41eb389ddbad9c9fd8df0de9b4b2 in llvm.

rdar://26780128
(cherry picked from commit 466f3ab46e3bd128c8cf770c1a7ba729716b99af)
diff --git a/utils/perf-training/lit.cfg b/utils/perf-training/lit.cfg
index 85d3551..eed87ba 100644
--- a/utils/perf-training/lit.cfg
+++ b/utils/perf-training/lit.cfg
@@ -7,7 +7,7 @@
 def getSysrootFlagsOnDarwin(config, lit_config):
     # On Darwin, support relocatable SDKs by providing Clang with a
     # default system root path.
-    if 'darwin' in config.target_triple:
+    if lit.util.isMacOSTriple(config.target_triple):
         try:
             out = lit.util.capture(['xcrun', '--show-sdk-path']).strip()
             res = 0
diff --git a/utils/perf-training/order-files.lit.cfg b/utils/perf-training/order-files.lit.cfg
index 75501f8..2e8f7ed 100644
--- a/utils/perf-training/order-files.lit.cfg
+++ b/utils/perf-training/order-files.lit.cfg
@@ -8,7 +8,7 @@
 def getSysrootFlagsOnDarwin(config, lit_config):
     # On Darwin, support relocatable SDKs by providing Clang with a
     # default system root path.
-    if 'darwin' in config.target_triple:
+    if lit.util.isMacOSTriple(config.target_triple):
         try:
             out = lit.util.capture(['xcrun', '--show-sdk-path']).strip()
             res = 0