config-fragments: drop old crosstool-ng toolchains

These toolchains are very old and cause a number of autobuilder failures
that doesn't happen with more recent toolchains:

Fixes (glibc 2.18 does not provide O_TMPFILE):
http://autobuild.buildroot.net/results/c49e8361a1d4406eefd8fc1b35c8e5b061aa403b

Fixes (x86 toolchain built without libquadmath):
http://autobuild.buildroot.net/results/2d9724f169ccd60c7feb1cb549f1e2e1e9219ac3/



Use Codesourcery ARM toolchain (GCC 4.8.3) to provide a test with a old GCC
version.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>