build: Really check for close_range() as intended

Signed-off-by: Simon McVittie <smcv@collabora.com>

libglnx.m4

@@ -4,6 +4,7 @@
 
 AC_DEFUN([LIBGLNX_CONFIGURE],
 [
+dnl This defines HAVE_DECL_FOO to 1 if found or 0 if not
 AC_CHECK_DECLS([
         renameat2,
         memfd_create,
@@ -19,6 +20,9 @@ AC_CHECK_DECLS([
 #include <linux/random.h>
 #include <sys/mman.h>
 ]])
+dnl This defines HAVE_FOO to 1 if found, or leaves it undefined if not:
+dnl not the same!
+AC_CHECK_FUNCS([close_range])
 
 AC_ARG_ENABLE(otmpfile,
               [AS_HELP_STRING([--disable-otmpfile],

meson.build

@@ -49,16 +49,16 @@ foreach check_function : check_functions
   )
   conf.set10('HAVE_DECL_' + check_function.underscorify().to_upper(), have_it)
 endforeach
-config_h = configure_file(
-  output : 'libglnx-config.h',
-  configuration : conf,
-)
 
 check_functions = [
   'close_range',
 ]
 foreach check_function : check_functions
+  if cc.has_function(check_function)
+    conf.set('HAVE_' + check_function.underscorify().to_upper(), 1)
+  endif
 endforeach
+
 config_h = configure_file(
   output : 'libglnx-config.h',
   configuration : conf,