[LyX/master] Fix syntax error whe testing old compilers

[Jean-Marc Lasgouttes]

commit 26b3674240f7739f1364657f93464151b7ca8f24
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Mon Dec 7 22:51:36 2015 +0100

    Fix syntax error whe testing old compilers

diff --git a/config/lyxinclude.m4 b/config/lyxinclude.m4
index 30697d7..d7ef249 100644
--- a/config/lyxinclude.m4
+++ b/config/lyxinclude.m4
@@ -319,7 +319,7 @@ if test x$GXX = xyes; then
   if test x$enable_cxx11 != xno ; then
     case $gxx_version in
       4.0*|4.1*|4.2*)
-         if x$enable_cxx11 = xyes; then
+         if test x$enable_cxx11 = xyes; then
             AC_ERROR([There is no C++11 support in gcc 4.2 or older])
          fi;;
       4.3*|4.4*|4.5*|4.6*)