The LIT test cases were migrated with the script provided by
Nikita Popov. Due to the size of the change it is split into
several parts.
Reviewed By: nemanja, nikic
Differential Revision: https://reviews.llvm.org/D135474
On PPC64, for a variadic function, if va_start is not called, it won't
access any variadic argument on stack, thus we can save stores of
registers used to pass arguments.
Differential Revision: https://reviews.llvm.org/D82361