FreeBSD/Linux Kernel Cross Reference
sys/contrib/libsodium/m4/ax_check_compile_flag.m4

     # ===========================================================================
     #   http://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
     # ===========================================================================
     #
     # SYNOPSIS
     #
     #   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS])
     #
     # DESCRIPTION
    #
    #   Check whether the given FLAG works with the current language's compiler
    #   or gives an error.  (Warnings, however, are ignored)
    #
    #   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
    #   success/failure.
    #
    #   If EXTRA-FLAGS is defined, it is added to the current language's default
    #   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
    #   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
    #   force the compiler to issue an error when a bad flag is given.
    #
    #   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
    #
    #   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
    #   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
    #
    # LICENSE
    #
    #   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
    #   Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
    #
    #   This program is free software: you can redistribute it and/or modify it
    #   under the terms of the GNU General Public License as published by the
    #   Free Software Foundation, either version 3 of the License, or (at your
    #   option) any later version.
    #
    #   This program is distributed in the hope that it will be useful, but
    #   WITHOUT ANY WARRANTY; without even the implied warranty of
    #   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
    #   Public License for more details.
    #
    #   You should have received a copy of the GNU General Public License along
    #   with this program. If not, see <https://www.gnu.org/licenses/>.
    #
    #   As a special exception, the respective Autoconf Macro's copyright owner
    #   gives unlimited permission to copy, distribute and modify the configure
    #   scripts that are the output of Autoconf when processing the Macro. You
    #   need not follow the terms of the GNU General Public License when using
    #   or distributing such scripts, even though portions of the text of the
    #   Macro appear in them. The GNU General Public License (GPL) does govern
    #   all other use of the material that constitutes the Autoconf Macro.
    #
    #   This special exception to the GPL applies to versions of the Autoconf
    #   Macro released by the Autoconf Archive. When you make and distribute a
    #   modified version of the Autoconf Macro, you may extend this special
    #   exception to the GPL to apply to your modified version as well.
    
    #serial 5
    
    AC_DEFUN([AX_CHECK_COMPILE_FLAG],
    [AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
    AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
    AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
      ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
      _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
      AC_TRY_LINK([#include <time.h>],
        [time_t x; int fodder = 0; if (fodder > -1000 && time(&x)) return (int) x],
        [AS_VAR_SET(CACHEVAR,[yes])],
        [AS_VAR_SET(CACHEVAR,[no])])
      _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
    AS_VAR_IF(CACHEVAR,yes,
      [m4_default([$2], :)],
      [m4_default([$3], :)])
    AS_VAR_POPDEF([CACHEVAR])dnl
    ])dnl AX_CHECK_COMPILE_FLAGS

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