Make VLAs usable, and make basic usage work correctly.  Also, add a 
simple test that actually does VLA codegen.

Note that despite the fact that the alloca isn't in the entry block, it 
should dominate all uses; this is guaranteed by the restrictions on goto 
into VLA scope in C99.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@61291 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed