Upgrade to GDB 7.6.1

Change-Id: I9865d7d941719ddc228b6e4dea9abf0d702e3653
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: David Schulz <david.schulz@digia.com>
gdb: Adjust path to python artifacts in build script.

Change-Id: I2d08d66d0f91a448e2a575387f34baaa8f91b560
Reviewed-by: Orgad Shaneh <orgads@gmail.com>