build: add function to build string of features

Add a CC_FEATURE_APPEND function that we can use to append the features
that are enabled/disabled. This will generate a single string in the
form "+FEATURE1 +FEATURE2 -FEATURE3".

Reviewed-by: Andreas Mohr <andim2@users.sf.net>

diff --git a/m4/features.m4 b/m4/features.m4
new file mode 100644 (file)
index 0000000..82a244f
--- /dev/null
+++ b/m4/features.m4
@@ -0,0 +1,48 @@
+#  Copyright (c) 2015 Lucas De Marchi <lucas.de.marchi@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 2 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 <http://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.
+#
+# CC_FEATURE_APPEND([FLAGS], [ENV-TO-CHECK], [FLAG-NAME])
+AC_DEFUN([CC_FEATURE_APPEND], [
+  AS_VAR_PUSHDEF([FLAGS], [$1])dnl
+  AS_VAR_PUSHDEF([ENV_CHECK], [$2])dnl
+  AS_VAR_PUSHDEF([FLAG_NAME], [$3])dnl
+
+  AS_CASE([" AS_VAR_GET(FLAGS) " ],
+          [*" FLAG_NAME "*], [AC_RUN_LOG([: FLAGS already contains FLAG_NAME])],
+          [
+           AS_IF([test "x$FLAGS" != "x"], [AS_VAR_APPEND(FLAGS, " ")])
+            AS_IF([test "x$ENV_CHECK" = "xyes"],
+                  [AS_VAR_APPEND(FLAGS, "+FLAG_NAME")],
+                  [AS_VAR_APPEND(FLAGS, "-FLAG_NAME")])
+          ]
+  )
+
+  AS_VAR_POPDEF([FLAG_NAME])dnl
+  AS_VAR_POPDEF([ENV_CHECK])dnl
+  AS_VAR_POPDEF([FLAGS])dnl
+])