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)

include/tradstdc.h

@@ -393,6 +393,17 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #endif
 #endif
 
+/*
+ * Give first priority to standard
+ */
+#ifndef ATTRNORETURN
+#if defined(__STDC_VERSION__) || defined(__cplusplus)
+#if (__STDC_VERSION__ > 202300L) || defined(__cplusplus)
+#define ATTRNORETURN [[noreturn]]
+#endif
+#endif
+#endif
+
 /*
  * Allow gcc2 to check parameters of printf-like calls with -Wformat;
  * append this to a prototype declaration (see pline() in extern.h).
@@ -406,7 +417,11 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #endif
 #if __GNUC__ >= 3
 #define UNUSED __attribute__((unused))
+#ifndef ATTRNORETURN
+#ifndef NORETURN
 #define NORETURN __attribute__((noreturn))
+#endif
+#endif
 #if (!defined(__linux__) && !defined(MACOS)) || defined(GCC_URWARN)
 /* disable gcc's __attribute__((__warn_unused_result__)) since explicitly
    discarding the result by casting to (void) is not accepted as a 'use' */
@@ -419,6 +434,12 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #endif
 #endif
 
+#ifdef _MSC_VER
+#ifndef ATTRNORETURN
+#define ATTRNORETURN __declspec(noreturn)
+#endif
+#endif
+
 #ifndef PRINTF_F
 #define PRINTF_F(f, v)
 #endif
@@ -428,6 +449,9 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #ifndef UNUSED
 #define UNUSED
 #endif
+#ifndef ATTRNORETURN
+#define ATTRNORETURN
+#endif
 #ifndef NORETURN
 #define NORETURN
 #endif
@@ -435,4 +459,5 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
 #define NONNULL
 #endif
 
+
 #endif /* TRADSTDC_H */