Create portable toolchain

This commit adds changes required for the toolchain to be
portable:

* Toolchain built is now static
* All SDK headers are installed into the toolchain itself
* All blobs from SDK are installed into toolchain itself
* Toolchain directory name is its GNU_TARGET_NAME by default

This also removes the need to specify the -L and -I flags
while building the actual software to include SDK libraries

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
Add an OPENSOURCE option

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
Instead of "OPENSOURCE" option, use "STANDALONE" with inverted meaning.

STANDALONE is the default.