Merge pull request #1545 from trofi/glibc-2.26

src/libmain/stack.cc: fix 'ucontext' usage on glibc-2.26

Author: edolstra

src/libmain/stack.cc

@@ -18,9 +18,9 @@ static void sigsegvHandler(int signo, siginfo_t * info, void * ctx)
     bool haveSP = true;
     char * sp = 0;
 #if defined(__x86_64__) && defined(REG_RSP)
-    sp = (char *) ((ucontext *) ctx)->uc_mcontext.gregs[REG_RSP];
+    sp = (char *) ((ucontext_t *) ctx)->uc_mcontext.gregs[REG_RSP];
 #elif defined(REG_ESP)
-    sp = (char *) ((ucontext *) ctx)->uc_mcontext.gregs[REG_ESP];
+    sp = (char *) ((ucontext_t *) ctx)->uc_mcontext.gregs[REG_ESP];
 #else
     haveSP = false;
 #endif