MT#55283 explicitly enable gcc optimisation

We rely on dpkg-buildflags to set -O2, but that may not be available on
the target system. Explicitly set -O3, and also enable LTO.

Change-Id: I593ec7ead08cb0a47922ba4db684b0292647f2bc

lib/lib.Makefile

@@ -62,6 +62,8 @@ ifneq ($(DBG),yes)
       LDFLAGS+=	$(shell dpkg-buildflags --get LDFLAGS)
       LDLIBS+=	$(shell dpkg-buildflags --get LDLIBS)
     endif
+    CFLAGS+=-O3 -flto=auto -ffat-lto-objects
+    LDFLAGS+=-flto=auto
   endif
 endif