support/testing: update basic toolchain to bootlin bleeding-edge 2018.11-1

support/testing: update basic toolchain to bootlin bleeding-edge 2018.11-1

Update the toolchain being used by the testsuite infra.

The new toolchain 2018.11-1 is based on gcc 8.2, uClibc-ng 1.0.30,
linux-headers 4.14 and binutils 2.31.1.
Enable BR2_TOOLCHAIN_HAS_THREADS_DEBUG that is now required.

The old toolchain 2017.05 is based on gcc 4.9, uClibc-ng 1.0.25,
linux-headers 3.10 and binutils 2.27.

Tested with gitlab
https://gitlab.com/kubu93/buildroot/pipelines/132376578

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>