Link libunwind to libgcc_s rather than libgcc
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 <3055038c414aef68bf32c33b8118623e7554e0f2@nvidia.com>

dropbox/libunwind,tony/libunwind,vtjnash/libunwind,rntz/libunwind,vtjnash/libunwind,krytarowski/libunwind,djwatson/libunwind,djwatson/libunwind,joyent/libunwind,wdv4758h/libunwind,rantala/libunwind,Chilledheart/libunwind,tony/libunwind,martyone/libunwind,tkelman/libunwind,wdv4758h/libunwind,unkadoug/libunwind,zliu2014/libunwind-tilegx,tkelman/libunwind,project-zerus/libunwind,unkadoug/libunwind,martyone/libunwind,vegard/libunwind,rogwfu/libunwind,rantala/libunwind,vtjnash/libunwind,vegard/libunwind,bo-on-software/libunwind,vegard/libunwind,fdoray/libunwind,bo-on-software/libunwind,joyent/libunwind,igprof/libunwind,dagar/libunwind,djwatson/libunwind,rogwfu/libunwind,zliu2014/libunwind-tilegx,martyone/libunwind,rntz/libunwind,fdoray/libunwind,atanasyan/libunwind,joyent/libunwind,dropbox/libunwind,Chilledheart/libunwind,pathscale/libunwind,zliu2014/libunwind-tilegx,rantala/libunwind,pathscale/libunwind,frida/libunwind,libunwind/libunwind,yuyichao/libunwind,libunwind/libunwind,rogwfu/libunwind,krytarowski/libunwind,atanasyan/libunwind,tony/libunwind,dagar/libunwind,evaautomation/libunwind,project-zerus/libunwind,dropbox/libunwind,evaautomation/libunwind,yuyichao/libunwind,yuyichao/libunwind,wdv4758h/libunwind,rntz/libunwind,Chilledheart/libunwind,frida/libunwind,krytarowski/libunwind,evaautomation/libunwind,igprof/libunwind,igprof/libunwind,unkadoug/libunwind,dagar/libunwind,tkelman/libunwind,bo-on-software/libunwind,project-zerus/libunwind,atanasyan/libunwind,fdoray/libunwind,pathscale/libunwind,frida/libunwind,libunwind/libunwind