The main difference between __va_start and __builtin_va_start is that
the address of the va_list has already been taken, and the va_list is
always a char*.

__va_end and __va_arg are not needed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204821 91177308-0d34-0410-b5e6-96231b3b80d8