libosmocore: add missing AC_LANG_SOURCE for current autoconf
autoconf >=2.68 demands the body of an AC_COMPILE_IFELSE to be wrapped in
an AC_LANG_SOURCE macro, otherwise outputs annoying warnings on the
invocation of `autoreconf -i`. this patch follows that demand.
diff --git a/configure.in b/configure.in
index 2e22bb2..b923a21 100644
--- a/configure.in
+++ b/configure.in
@@ -24,7 +24,7 @@
saved_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -fvisibility=hidden "
AC_MSG_CHECKING([if ${CC} supports -fvisibility=hidden])
-AC_COMPILE_IFELSE([char foo;],
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([char foo;])],
[ AC_MSG_RESULT([yes])
SYMBOL_VISIBILITY="-fvisibility=hidden"],
AC_MSG_RESULT([no]))