Bugfix: Actually create the build directory

Due to a typo, llvm-build would fail to create the build directory if it didn't
exist (and subsequently failed to cd to it and started building in the wrong
place). This fixes the typo, and also runs the mkdir with safe_run, so we can
bail out if something goes wrong.

Change-Id: I9ffe72a04e9e0643bb37298bf7668d39c2f3600e
1 file changed