configure: use AX_APPEND_COMPILE_FLAGS to detect supported warning flags
[lttng-tools.git] / m4 / ax_append_flag.m4
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
33 AC_DEFUN([AX_APPEND_FLAG],
34 [dnl
35 AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_SET_IF
36 AS_VAR_PUSHDEF([FLAGS], [m4_default($2,_AC_LANG_PREFIX[FLAGS])])
37 AS_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 ])
49 AS_VAR_POPDEF([FLAGS])dnl
50 ])dnl AX_APPEND_FLAG
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