AX_APPEND_FLAG: fix regression

AX_APPEND_FLAG has changed behaviour compared to earlier versions: it
adds the FLAG also when the variable contains FLAG. I traced down the
altered behaviour to the two lines

 [case " AS_VAR_GET(FLAGS) " in
    *" $1 "*)

which have changed to

  AS_CASE([AS_VAR_GET(FLAGS)],
    ["* $1 *|*$1"]

besides that AS_CASE is used (which is good imho) the pattern has
changed and the space around FLAGS in the first argument of AS_CASE has
gone. This means that e.g. if FLAGS is "alpha beta gamma" that will not
match the pattern "* $1 *|*$1" for $1 being any of 'alpha', 'beta', or
'gamma'. I think that is unexpected behaviour.

This patch restores the original semantics.

For further details can be found at:

  http://lists.gnu.org/archive/html/autoconf-archive-maintainers/2015-02/msg00000.html

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 2d06e08..38653f8 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,8 @@
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+  AX_APPEND_FLAG: Fix a regression introduced in the previous release.
+
 * Noteworthy changes in release 2015.02.04 (2015-02-04) [stable]
 
   AX_OPENMP: Test that we can actually #include <omp.h> successfully.