Instead of "OPENSOURCE" option, use "STANDALONE" with inverted meaning.

STANDALONE is the default.
Update crosstool-NG (gdb fixes for qemu).
README: Update for new standalone build mode.
Install vendor SDK in toolchain sysroot.

Also, do that when installing vendor SDK, not when installing toolchain.
Name subdir targets with underscore prefix (they're internal targets).
Install libhal to sysroot too, where it can be found.

Also, add phony target aliases to easily rebuild particular one.