Add option for architecture in Makefile

In this merge request:

• Add an option to add gcc architecture option in main Makefile (-m32, -m64, etc.)
• Use a more idiomatic way to call sub Makefiles

Makefile

 # ARCH_OPT is the gcc architecture option (probably -m32 or -m64)
-export ARCH_OPT="-m64"
+export ARCH_OPT="-m32"
 MAKE="make"
 
 build: