- Fix configure test for nonstring attribute so that it does not

accept when the compiler prints a warning about an unknown
  attribute.

acx_nlnetlabs.m4

@@ -2,7 +2,9 @@
 # Copyright 2009, Wouter Wijngaards, NLnet Labs.   
 # BSD licensed.
 #
-# Version 50
+# Version 51
+# 2025-11-06 Fix ACX_CHECK_NONSTRING_ATTRIBUTE to reject clang, that prints
+#	     a warning for 'unknown attribute' when nonstring is used.
 # 2025-09-29 add ac_cv_func_malloc_0_nonnull as a cache value for the malloc(0)
 #            check by ACX_FUNC_MALLOC.
 # 2025-09-29 add ACX_CHECK_NONSTRING_ATTRIBUTE, AHX_CONFIG_NONSTRING_ATTRIBUTE.
@@ -535,6 +537,9 @@ dnl result in HAVE_ATTR_NONSTRING.
 dnl Make sure you include AHX_CONFIG_NONSTRING_ATTRIBUTE also.
 AC_DEFUN([ACX_CHECK_NONSTRING_ATTRIBUTE],
 [AC_REQUIRE([AC_PROG_CC])
+AC_REQUIRE([ACX_CHECK_ERROR_FLAGS])
+BAKCFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS $ERRFLAG"
 AC_MSG_CHECKING(whether the C compiler (${CC-cc}) accepts the "nonstring" attribute)
 AC_CACHE_VAL(ac_cv_c_nonstring_attribute,
 [ac_cv_c_nonstring_attribute=no
@@ -546,6 +551,7 @@ struct test {
    struct test t = { "1" };
    (void) t;
 ]])],[ac_cv_c_nonstring_attribute="yes"],[ac_cv_c_nonstring_attribute="no"])
+CFLAGS="$BAKCFLAGS"
 ])
 
 dnl Setup ATTR_NONSTRING config.h parts.

configure

@@ -6949,6 +6949,9 @@ printf "%s\n" "#define HAVE_ATTR_UNUSED 1" >>confdefs.h
 fi
 
 
+
+BAKCFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS $ERRFLAG"
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the C compiler (${CC-cc}) accepts the \"nonstring\" attribute" >&5
 printf %s "checking whether the C compiler (${CC-cc}) accepts the \"nonstring\" attribute... " >&6; }
 if test ${ac_cv_c_nonstring_attribute+y}
@@ -6981,6 +6984,7 @@ else $as_nop
   ac_cv_c_nonstring_attribute="no"
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
+CFLAGS="$BAKCFLAGS"
 
 fi
 
@@ -7059,7 +7063,14 @@ else $as_nop
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
  #include <stdio.h>
-__attribute__((noreturn)) void f(int x) { printf("%d", x); }
+#ifdef STDC_HEADERS
+# include <stdlib.h>
+#else
+# ifdef HAVE_STDLIB_H
+#  include <stdlib.h>
+# endif
+#endif
+__attribute__((noreturn)) void f(int x) { printf("%d", x); exit(1); }
 
 int
 main (void)

doc/Changelog

@@ -2,6 +2,9 @@
 	- Fix add comment to worker_handle_request function that explain it.
 	- Fix configure test for noreturn attribute so it compiles without
 	  warning.
+	- Fix configure test for nonstring attribute so that it does not
+	  accept when the compiler prints a warning about an unknown
+	  attribute.
 
 4 November 2025: Wouter
 	- Fix dns64 log output to log the default instead of a null string.