The kernel changes for a 64-bit time_t on 32-bit architectures
resulted in <asm/socket.h> indirectly including <linux/posix_types.h>.
The latter is not namespace-clean for the POSIX version of
<sys/socket.h>.
This issue has persisted across several Linux releases, so this commit
creates our own copy of the SO_* definitions for !__USE_MISC mode.
The new test socket/tst-socket-consts ensures that the copy is
consistent with the kernel definitions (which vary across
architectures). The test is tricky to get right because CPPFLAGS
includes include/libc-symbols.h, which in turn defines _GNU_SOURCE
unconditionally.
Tested with build-many-glibcs.py. I verified that a discrepancy in
the definitions actually results in a failure of the
socket/tst-socket-consts test.
(cherry picked from commit 7854ebf8ed18180189c335f6f499fe9322458f0b)
845278f2c6