Request for review: Fix build-llvm.pl

Summary:
- Stop to try to rebuild llvm on each invocation by removing the invalid library entry libLLVMArchive.a which no longer exists.
- Remove the useless ranlib invocation. "libtools -static" automatically takes care of the archive table of content.

CC: lldb-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2296