[dwarf] The sword() function in Gexpr.c doesn't do what's intended.

Yes, it casts to signed, but then converts right back to
unsigned via the return type.  Fixed thus.

Signed-off-by: Richard Henderson <rth@redhat.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
diff --git a/include/libunwind-x86_64.h b/include/libunwind-x86_64.h
index 804600c..a87b57e 100644
--- a/include/libunwind-x86_64.h
+++ b/include/libunwind-x86_64.h
@@ -48,6 +48,7 @@
 #define UNW_TDEP_CURSOR_LEN	127
 
 typedef uint64_t unw_word_t;
+typedef int64_t unw_sword_t;
 
 typedef long double unw_tdep_fpreg_t;