Check for missing LUAC in configure rather than make, make it precious

configure.ac

@@ -1629,7 +1629,10 @@ then
   else
       AC_MSG_ERROR([Could not find lua. Lua is needed for some interfaces (rc, telnet, http) as well as many other custom scripts. Use --disable-lua to ignore this error.])
   fi
-  AC_PATH_PROG(LUAC, luac)
+  AC_ARG_VAR([LUAC], [LUA byte compiler])
+  AC_PATH_PROG(LUAC, luac, [
+    AC_MSG_ERROR([Could not find the LUA byte compiler.])
+  ])
 fi
 AM_CONDITIONAL(BUILD_LUA, [test "${have_lua}" = "yes"])
 

share/Makefile.am

@@ -193,10 +193,6 @@ luac_verbose_ = $(luac_verbose_$(AM_DEFAULT_VERBOSITY))
 luac_verbose_0 = @echo "  LUAC   $@";
 
 .lua.luac:
-	$(AM_V_at)if test -z "$(LUAC)"; then \
-		echo "LUA byte compiler missing." >&2; \
-		exit 1 ; \
-	fi
 	$(AM_V_at)for f in $(EXTRA_DIST); do \
 		test "$(srcdir)" = . || f="$(srcdir)/$$f"; \
 		if test $$f = $<; then \