expand support for noreturn declarations

Although gcc specifies support for declaring a function as
noreturn after the function name and parameters, other compilers
do so via an attribute at the start of the declaration. Add some
macro support for the attribute-at-the-beginning method:
  o MS Visual Studio compiler
  o Upcoming C23 standard (untested at this point)

src/end.c

@@ -596,7 +596,7 @@ fixup_death(int how)
 DISABLE_WARNING_FORMAT_NONLITERAL
 
 /*VARARGS1*/
-void
+ATTRNORETURN void
 panic VA_DECL(const char *, str)
 {
     VA_START(str);
@@ -1780,7 +1780,7 @@ container_contents(
 }
 
 /* should be called with either EXIT_SUCCESS or EXIT_FAILURE */
-void
+ATTRNORETURN void
 nh_terminate(int status)
 {
     g.program_state.in_moveloop = 0; /* won't be returning to normal play */