[lldb] Use foo is None instead of not foo in darwin.py

Explicitly compare to None when checking the triple's components so we
don't bail out when one of them is the empty string.

lldb/packages/Python/lldbsuite/test/builders/darwin.py

@@ -43,12 +43,12 @@ def get_triple():
 
     # Get the SDK from the os and env.
     sdk = lldbutil.get_xcode_sdk(os, env)
-    if not sdk:
+    if sdk is None:
         return None, None, None, None
 
     # Get the version from the SDK.
     version = lldbutil.get_xcode_sdk_version(sdk)
-    if not version:
+    if version is None:
         return None, None, None, None
 
     return vendor, os, version, env
@@ -86,7 +86,7 @@ def getArchCFlags(self, arch):
         """Returns the ARCH_CFLAGS for the make system."""
         # Get the triple components.
         vendor, os, version, env = get_triple()
-        if not vendor or not os or not version or not env:
+        if vendor is None or os is None or version is None or env is None:
             return ""
 
         # Construct the triple from its components.