package/prboom: disable for Sourcery CodeBench SH 2012.09

package/prboom: disable for Sourcery CodeBench SH 2012.09

Building prboom with the external Sourcery CodeBench SH 2012.09 toolchain
fails with an internal compiler error:

r_fps.c: In function 'R_StopAllInterpolations':
r_fps.c:296:1: internal compiler error: Segmentation fault

Make the toolchain unavailable for building prboom.

Fixes:
http://autobuild.buildroot.net/results/2f1/2f14075e22b420cc3fdaaa2231494f2829f040ec/
http://autobuild.buildroot.net/results/d30/d3030fea0b3b8693be640754774e50ac064f8c89/
http://autobuild.buildroot.net/results/b5b/b5b90a03fc47f3771803cb474e0ea9671b5c4667/

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>