add lib_amazon makefile command that was missing and required to buil…

…d amazon_freertos SDK

new step after fix apply:
make lib_amazon
make is

project/realtek_amebaz2_v0_example/GCC-RELEASE/Makefile.amazon

@@ -5,6 +5,9 @@ LBITS := $(shell getconf LONG_BIT)
 
 include toolchain.mk
 
+.PHONY: lib_amazon
+lib_amazon: toolchain
+	@$(MAKE) -f lib_amazon.mk
 
 .PHONY: is
 is: toolchain