configure: use AX_APPEND_COMPILE_FLAGS to detect supported warning flags
[deliverable/lttng-tools.git] / m4 / ax_append_flag.m4
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1# ===========================================================================
2# https://www.gnu.org/software/autoconf-archive/ax_append_flag.html
3# ===========================================================================
4#
5# SYNOPSIS
6#
7# AX_APPEND_FLAG(FLAG, [FLAGS-VARIABLE])
8#
9# DESCRIPTION
10#
11# FLAG is appended to the FLAGS-VARIABLE shell variable, with a space
12# added in between.
13#
14# If FLAGS-VARIABLE is not specified, the current language's flags (e.g.
15# CFLAGS) is used. FLAGS-VARIABLE is not changed if it already contains
16# FLAG. If FLAGS-VARIABLE is unset in the shell, it is set to exactly
17# FLAG.
18#
19# NOTE: Implementation based on AX_CFLAGS_GCC_OPTION.
20#
21# LICENSE
22#
23# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
24# Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
25#
26# Copying and distribution of this file, with or without modification, are
27# permitted in any medium without royalty provided the copyright notice
28# and this notice are preserved. This file is offered as-is, without any
29# warranty.
30
31#serial 8
32
33AC_DEFUN([AX_APPEND_FLAG],
34[dnl
35AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_SET_IF
36AS_VAR_PUSHDEF([FLAGS], [m4_default($2,_AC_LANG_PREFIX[FLAGS])])
37AS_VAR_SET_IF(FLAGS,[
38 AS_CASE([" AS_VAR_GET(FLAGS) "],
39 [*" $1 "*], [AC_RUN_LOG([: FLAGS already contains $1])],
40 [
41 AS_VAR_APPEND(FLAGS,[" $1"])
42 AC_RUN_LOG([: FLAGS="$FLAGS"])
43 ])
44 ],
45 [
46 AS_VAR_SET(FLAGS,[$1])
47 AC_RUN_LOG([: FLAGS="$FLAGS"])
48 ])
49AS_VAR_POPDEF([FLAGS])dnl
50])dnl AX_APPEND_FLAG
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