Fix sparc64 build.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>

diff -Nur libsigsegv-2.10.orig/src/fault-linux-sparc.h libsigsegv-2.10/src/fault-linux-sparc.h
--- libsigsegv-2.10.orig/src/fault-linux-sparc.h	2009-08-01 17:06:49.000000000 +0200
+++ libsigsegv-2.10/src/fault-linux-sparc.h	2015-11-29 11:55:29.000000000 +0100
@@ -27,4 +27,8 @@
    (see also <asm/sigcontext.h>)
    are quite different types.  */
 
+#if __WORDSIZE == 64
+#define SIGSEGV_FAULT_STACKPOINTER  ((ucontext_t *) ucp)->uc_mcontext.mc_gregs[REG_O6]
+#else
 #define SIGSEGV_FAULT_STACKPOINTER  ((ucontext_t *) ucp)->uc_mcontext.gregs[REG_O6]
+#endif