linuxthreads: enable unwinding over signal frames

linuxthreads use a helper function to invoke signal handlers, this
function needs stack unwinding information to enable stack unwinding
from signal handlers over signal frames.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

libpthread/linuxthreads/Makefile.in

@@ -16,6 +16,8 @@ libpthread_OUT := $(top_builddir)libpthread/linuxthreads
 
 -include $(libpthread_DIR)/sysdeps/$(TARGET_ARCH)/Makefile.arch
 
+CFLAGS-signals.c = -fexceptions -fasynchronous-unwind-tables
+
 libpthread_SRC := \
 	attr.c cancel.c condvar.c errno.c events.c join.c lockfile.c manager.c \
 	mutex.c pt-machine.c ptfork.c pthread.c ptlongjmp.c \