define G_DISABLE_ASSERT unless --enable-debug is specified

* turns out that glib's g_assert() does not depend on NDEBUG like Standard C's assert()
* this disables assertions in release builds and should speed up things slightly

configure.ac

@@ -23,6 +23,10 @@ AC_CANONICAL_HOST
 
 AX_CHECK_ENABLE_DEBUG
 AM_CONDITIONAL(DEBUG, [test x$ax_enable_debug != xno])
+if [[ x$ax_enable_debug = xno ]]; then
+	# glib does not look at NDEBUG
+	AC_DEFINE(G_DISABLE_ASSERT, 1, [Disable g_assert()])
+fi
 
 # Use the user provided CXXFLAGS for Scintilla as well.
 # This makes sure that the same optimizations are applied

src/expressions.c

@@ -86,7 +86,7 @@ teco_int_t
 teco_expressions_pop_num(guint index)
 {
 	teco_int_t n = 0;
-	teco_operator_t op = teco_expressions_pop_op(0);
+	G_GNUC_UNUSED teco_operator_t op = teco_expressions_pop_op(0);
 
 	g_assert(op == TECO_OP_NUMBER);