Fix CC_FOR_BUILD detection
diff --git a/configure.ac b/configure.ac
index c71c5bd..fed23c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -39,7 +39,7 @@ PKG_PROG_PKG_CONFIG
dnl Build native compiler needed for makekeys
AC_ARG_VAR([CC_FOR_BUILD], [Build native C compiler program])
-if test "x$CC_FOR_BUILD" != x; then
+if test "x$CC_FOR_BUILD" = x; then
if test "$cross_compiling" != no; then
AC_PATH_PROGS([CC_FOR_BUILD], [gcc cc], [cc])
else