Presently, Valgrind (non-client) code that wants to use the stat

Presently, Valgrind (non-client) code that wants to use the stat
family of syscalls is impossible to write in a way that's portable and
correct.  On some targets (eg x86-linux) you need to do sys_stat64 and
receive the results in a 'struct vki_stat64'.  But on other targets
(eg amd64-linux) neither sys_stat64 nor 'struct vki_stat64' exist.

This commit adds a new type, 'struct vg_stat', which contains 64 bit
fields in all the right places, and makes VG_(stat) and VG_(fstat) use
it.  This means callers to the two functions no longer need to worry
about the is-it-64-bit-clean-or-not question, since these routines
reformat the received data into a'struct vg_stat'.  Kind of like what
glibc must have been doing for decades.

This (indirectly) fixes a bug on x86-linux, in which m_debuginfo would
sometimes fail to read debug info, due to VG_(di_notify_mmap) using
VG_(stat) (hence sys_stat) on the file, which failed, and when in fact
it should have used sys_stat64.  Bug reported and tracked down by
Marc-Oliver Straub.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@8522