This patch addresses a 64-bit PowerPC ELF ABI compatibility issue with

varargs parameter passing.

A strict reading of the ABI indicates that any argument with alignment greater
than 8 may require skipping doublewords in the parameter save area to align
the argument, and hence require skipping GPRs.  In practice, this is not done
by GCC.  The alignment restriction is used for internal alignment of a
structure, but a structure with 16-byte alignment, for example, is not
itself 16-byte aligned in the parameter save area.  Although this is messy,
it has become the de facto standard used in building existing libraries.

My initial varargs support followed the ABI language, but not the de facto
standard.  Running the GCC compatibility test suite exposed this issue, and
indeed showed that LLVM didn't pass parameters self-consistently with my
original logic.  Removing the additional alignment logic allows the affected
tests to now pass.

I modified the ppc64-varargs-struct.c test case to remove the existing test
for generation of alignment code, which is no longer appropriate.

Built and tested on powerpc64-unknown-linux-gnu with no new regressions.

llvm-svn: 166805