auto/clang: Added NJS_NONSTRING macro.

This is a wrapper around __attribute__((nonstring)). Traditionally this
was used to mark char array variables that intentionally lacked a
terminating NUL byte, this would then cause warnings to either be
quelled or emitted for various memory/string functions.

GCC 15 introduced a new warning, Wunterminated-string-initialization,
which will always warn on things like

  static const char hex[16] = "0123456789ABCDEF";

However this is very much intentionally not NUL terminated.

The above attribute also quells this new warning (which is also enabled
by -Wextra).

So the above example would become

  static const char hex[16] NJS_NONSTRING = "0123456789ABCDEF";

Link: <https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=44c9403ed1833ae71a59e84f9e37af3182be0df5>
Link: <https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=622968990beee7499e951590258363545b4a3b57>
Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178#c21>
Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000

auto/clang

@@ -172,6 +172,20 @@ njs_feature_test="__attribute__((no_sanitize(\"undefined\"))) int main(void) {
 . auto/feature
 
 
+njs_feature="GCC __attribute__ nonstring"
+njs_feature_name=NJS_HAVE_GCC_ATTRIBUTE_NONSTRING
+njs_feature_run=
+njs_feature_incs=
+njs_feature_libs=
+njs_feature_test="int main(void) {
+                      static const char str[3] __attribute__((nonstring)) =
+                          \"ABC\";
+
+                      return !!str[0];
+                  }"
+. auto/feature
+
+
 njs_feature="Address sanitizer"
 njs_feature_name=NJS_HAVE_ADDRESS_SANITIZER
 njs_feature_run=no

src/njs_clang.h

@@ -162,6 +162,14 @@ njs_leading_zeros64(uint64_t x)
 #endif
 
 
+#if (NJS_HAVE_GCC_ATTRIBUTE_NONSTRING)
+#define NJS_NONSTRING      __attribute__((nonstring))
+
+#else
+#define NJS_NONSTRING
+#endif
+
+
 #if (NJS_CLANG)
 /* Any __asm__ directive disables loop vectorization in GCC and Clang. */
 #define njs_pragma_loop_disable_vectorization  __asm__("")