Makefile: adding config variable for Os/O2/O3 compilation
fix build errors with -O2 flag
update defconfig
Makefile: improved build flags
Makefile: use -fno-pic to compile modules
without this flag kernel can't load modules
Makefile: more build flags
fix wrong build flags setup and add more build flags
Makefile: improve build flags
Makefile: enable graphite loop optimization