Here's version 2 (filename version 6, in honor of glibc ;) of the
memset code. I fixed a bug in the logic for coverage of the tail (the
part past what's covered by the loop) for some values of n and
alignments, and cleaned up the __GNUC__ usage a bit to use less
#ifdeffery. The remaining test at the top for the __GNUC__ version is
ugly, I admit, and should possibly just be removed and replaced by a
configure check to add -D__may_alias__= to the CFLAGS if the compiler
defines __GNUC__ but does not recognize __attribute__((__may_alias__))
-- opinions on this?

Rich