Add back SA_NODEFER

It turns out that you can only send one SIGINT without it. Duh. I'm an
idiot.

However, it actually may cause problems for editline, so only use it
when editline is not activated.

Signed-off-by: Gavin D. Howard <gavin@gavinhoward.com>

src/vm.c

@@ -121,6 +121,8 @@ bc_vm_jmp(void)
 static void
 bc_vm_sig(int sig)
 {
+	(void) write(STDERR_FILENO, "Z", 1);
+
 #if BC_ENABLE_EDITLINE
 	// Editline needs this to resize the terminal. This also needs to come first
 	// because a resize always needs to happen.
@@ -214,7 +216,7 @@ bc_vm_sigaction(void)
 	struct sigaction sa;
 
 	sigemptyset(&sa.sa_mask);
-	sa.sa_flags = 0;
+	sa.sa_flags = BC_ENABLE_EDITLINE ? 0 : SA_NODEFER;
 
 	// This mess is to silence a warning on Clang with regards to glibc's
 	// sigaction handler, which activates the warning here.