Fix va_arg on x86-64 for a struct containing a single int128_t.  PR16248

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@183590 91177308-0d34-0410-b5e6-96231b3b80d8
When we're compiling with -pg make sure to link with gcrt1.o on linux. Be
sure to do this always, this matches the behavior for the gcc driver.

Fixes PR16251.

Based on a patch by Qiao Yang.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@183591 91177308-0d34-0410-b5e6-96231b3b80d8