manual/ipc.texi: Fix AC-safety notes.

The function sem_close is AC-unsafe because lll_lock*
leaks a lock (aculock) and not because of twalk.
PowerPC: Fix --disable-multi-arch builds

This patch fixes some powerpc32 and powerpc64 builds with
--disable-multi-arch option along with different --with-cpu=powerN.
It cleanups the Implies directories by removing the multiarch
folder for non multiarch config and also fixing two assembly
implementations: powerpc64/power7/strncat.S that is calling the
wrong strlen; and power8/fpu/s_isnan.S that misses the hidden_def and
weak_alias directives.
Move __PTHREAD_SPINS definition to architecture specific header

This patch moves the __PTHREAD_SPINS definition to arch specific header
since pthread_mutex_t layout is also arch specific.  This leads to no
need to defining __PTHREAD_MUTEX_HAVE_ELISION and thus removing of the
undefined compiler warning.
Use statvfs64() for pathconf(_PC_NAME_MAX).

pathconf(_PC_NAME_MAX) was implemented on top of statfs().  The 32bit
version therefore fails EOVERFLOW if the filesystem blockcount is
sufficiently large.

Most pathconf() queries use statvfs64(), which avoids this issue.  This
patch modifies pathconf(_PC_NAME_MAX) to do likewise.