Use shallow clones in build-llvm.py.

Summary:
This makes cloning (and therefore the whole build) faster.
The checkout step goes from ~4m to ~30s on my host.

Reviewers: tfiala

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D17425

llvm-svn: 262513

lldb/scripts/Xcode/lldbbuild.py

@@ -65,7 +65,7 @@ def status (self):
     def diff (self):
         return run_in_directory(["git", "diff"], self.spec['root'])
     def check_out (self):
-        run_in_directory(["git", "clone", self.spec['url'], self.spec['root']], lldb_source_path())
+        run_in_directory(["git", "clone", "--depth=1", self.spec['url'], self.spec['root']], lldb_source_path())
         run_in_directory(["git", "fetch", "--all"], self.spec['root'])
         run_in_directory(["git", "checkout", self.spec['ref']], self.spec['root'])