Make various fixes to allow meta-toolchain to build

:Release Notes:
Make various fixes to allow the meta-toolchain target to build.

:Detailed Notes:
Also set more sensible defaults for SDK variables.

:Testing Performed:
Successfully built meta-toolchain target.
Verified toolchain use independently of the OE build environment.

:QA Notes:

:Issues Addressed:
[ES-803]   Unable to build meta-toolchain
[BHV-7334] CCC: Fix meta-toolchain build issue

Open-webOS-DCO-1.0-Signed-off-by: Iyad Qumei <iyad.qumei@lge.com>

Change-Id: Iee90666c0fa9eacf8669fa79efe74ff01669c35b
Reviewed-on: https://g2g.palm.com/5530
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: DCO Verification
Build: Susan Montooth <susan.montooth@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>