package/gcc: add support for gcc 8.1.0

package/gcc: add support for gcc 8.1.0

Remove 0860-cilk-fix-build-without-wchar.patch since cilk has
been removed from gcc.

Rebase 0900-remove-selftests.patch on gcc 8.1.0

Remove upstream patches 0001-m68k-coldfire-pr68467.patch and
0892-microblaze-Revert.patch.

Use bz2 release tarball only for gcc 4.9 since all other version
now use xz tarball.

Runtime tested on x86_64 with binutils 2.30, gcc 8.1.0,
kernel headers 4.14 and glibc 2.27.

Buildtime tested with glibc with all supported architectures.

Buildtime tested on x86_64 with musl and uClibc-ng

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