+fi # cf_cv_posix_visible
+
+])dnl
+dnl ---------------------------------------------------------------------------
+dnl CF_POSIX_VISIBLE version: 1 updated: 2018/12/31 20:46:17
+dnl ----------------
+dnl POSIX documents test-macros which an application may set before any system
+dnl headers are included to make features available.
+dnl
+dnl Some BSD platforms (originally FreeBSD, but copied by a few others)
+dnl diverged from POSIX in 2002 by setting symbols which make all of the most
+dnl recent features visible in the system header files unless the application
+dnl overrides the corresponding test-macros. Doing that introduces portability
+dnl problems.
+dnl
+dnl This macro makes a special check for the symbols used for this, to avoid a
+dnl conflicting definition.
+AC_DEFUN([CF_POSIX_VISIBLE],
+[
+AC_CACHE_CHECK(if the POSIX test-macros are already defined,cf_cv_posix_visible,[
+AC_TRY_COMPILE([#include <stdio.h>],[
+#if defined(__POSIX_VISIBLE) && ((__POSIX_VISIBLE - 0L) > 0) \
+ && defined(__XSI_VISIBLE) && ((__XSI_VISIBLE - 0L) > 0) \
+ && defined(__BSD_VISIBLE) && ((__BSD_VISIBLE - 0L) > 0) \
+ && defined(__ISO_C_VISIBLE) && ((__ISO_C_VISIBLE - 0L) > 0)
+#error conflicting symbols found
+#endif
+],[cf_cv_posix_visible=no],[cf_cv_posix_visible=yes])
+])