Link libunwind to libgcc_s rather than libgcc

For some architectures, -lgcc and -lgcc_s are not equivalent. On ARM for
example, libgcc_s.so.1 contains some symbols needed by libunwind which
are not present in libgcc.

This causes the following link error when building the X.Org X server
with libunwind support:

	  CCLD     Xorg
	/usr/lib/libunwind.so: undefined reference to `__aeabi_unwind_cpp_pr0'
	/usr/lib/libunwind.so: undefined reference to `__aeabi_unwind_cpp_pr1'

Linking against libgcc_s explicitly solves this problem.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Use helper to walk past the syscall frames on FreeBSD/x86, similar to FreeBSD/x86_64.

The syscall trampolines in FreeBSD libc do not have unwind annotations.
Adjust use_prev_instr for syscall and frame-chain frames.

Mark frames which are unwound with the frame-chain walker or
syscall frame code, as non-interrupted.  The return PC in the frame
points to the instruction after the call.
Correct name returned by get_proc_name() for some frames.

Fix returning the name of the function containing the frame PC,
for the non-interrupted frames.  The symbol lookup code should
take use_prev_instr value into account, otherwise it could return
the name of the function adjacent to the caller.
Remove unnecessary calls to labs()

Greetings,

Roman reports that Clang warns on unnecessary calls to labs():

  taking the absolute value of unsigned type 'unw_word_t' (aka
'unsigned long') has no effect [-Werror,-Wabsolute-value]

Since rs->reg[...].val is unw_word_t and unsigned on all platforms,
this patch removes the unnecessary calls to labs().

Tested on Linux x86_64, no regressions.

Thanks,
--
Paul Pluzhnikov
Fix empty structs in libunwind-x86_64.h

Hi,

there is a compilation issue with Clang and latest libunwind - It's
about "typedef struct unw_tdep_save_loc" and one more struct:

include/libunwind-x86_64.h:111:9: error: empty struct has size 0 in C,
size 1 in C++ [-Werror,-Wextern-c-compat]

The solution is very simple:
Fix compiler warnings when UNW_DEBUG is enabled

Newer versions of gcc complain when ALWAYS_INLINE is used without
inline.