(1) Fix warnings.
This is a bulk update to fix all the warnings that were causing
build failures with -Werror on hppa.
The most egregious problems are in dl-fptr.c which needs to be
entirely rewritten, thus I've used -Wno-error for that.
(2) Fix conformance errors.
The sysdep.c file had __syscall_error and syscall in one file
which caused conformance issues by including syscall when
__syscall_error was linked to. The fix is obviously to split
the file and use syscall.c to implement syscall.
This sets __HAVE_64B_ATOMICS if provided. It also sets
USE_ATOMIC_COMPILER_BUILTINS to true if the existing atomic ops use the
__atomic* builtins (aarch64, mips partially) or if this has been
tested (x86_64); otherwise, this is set to false so that C11 atomics will
be based on the existing atomic operations.
