Standalone build: add support for Link Time Optimization

Add is_lto option

Change-Id: Ibe5b5e092ab475047be539cca86f1062a43209d3
diff --git a/gn/standalone/BUILD.gn b/gn/standalone/BUILD.gn
index 1866a79..9e1b227 100644
--- a/gn/standalone/BUILD.gn
+++ b/gn/standalone/BUILD.gn
@@ -75,7 +75,7 @@
     "-Werror",
   ]
 
-  if (!is_wasm) {
+  if (!is_wasm && !is_lto) {
     cflags += [ "-Wa,--noexecstack" ]
   }
 
@@ -87,6 +87,11 @@
     ]
   }
 
+  if (is_lto) {
+    cflags += [ "-flto=full" ]
+    ldflags += [ "-flto=full" ]
+  }
+
   if (current_cpu == "arm") {
     cflags += [
       "-march=armv7-a",