tilegx32: avoid a a -Werror warning from unwinding

The _Unwind_GetCFA() routine returns a 64-bit value,
which we interpret as a pointer.  Add an intermediate
cast to long so that in ILP32 mode we don't get a warning
about casting a wrong-sized integer to a pointer.
tilegx: fix sysdep.h to avoid a redefinition warning

The symbol for HAVE_CLOCK_GETTIME_VSYSCALL was being
only conditionally defined under [SHARED].  However, it turns
out this causes a preprocessor symbol redefinition warning
when building clock_gettime.o.  Move the symbol definition
down to make it unconditional, like other platforms do.
linux/clock_settime: remove unnecessary vDSO definitions

These definitions were added back before __ASSUME_POSIX_CPU_TIMERS
was removed.  There used to be a vsyscall to clock_getres() in
maybe_syscall_settime_cpu(), but that function was removed in commit
26889eac.  The presence of the vsyscall definitions means that platforms
that don't provide clock_getres as a vsyscall hit a symbol redefinition
warning in this file, becoming fatal with -Werror.  Removing the
vsyscall definitions is the obvious fix.

No change to generated code on x86_64.
tile: add no-op fe*() routines for libc internal use

These avoid having tile generate real calls to the no-op
functions, which then causes linknamespace test failures.

It might make sense to factor all of these out into a common
header that can be shared by tile, microblaze, etc., but for
now just fix the test failures.