Pass compiler arguments in the create_ll.sh script

Summary:
Occasionally you need an include or similar things to be configured
when making a new testcase. Allow passing these to the script and down to the
compiler calls.

Reviewers: grosser, Meinersbur, bollu

Reviewed By: Meinersbur

Subscribers: bollu, llvm-commits, pollydev

Differential Revision: https://reviews.llvm.org/D46359

llvm-svn: 331364