toolchain: allow disabling packages affected by gcc bug 85180

toolchain: allow disabling packages affected by gcc bug 85180

Works around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85180 which
is an issue where the Microblaze architecture had code that caused a
infinite recursion while optimizing in versions of GCC earlier than
8.x. More BR discussion can be found on this thread.
http://buildroot-busybox.2317881.n4.nabble.com/autobuild-buildroot-net-Build-results-for-2018-04-25-td192721.html

Resolves:
http://autobuild.buildroot.net/results/b42d68c66d8ea035845a28c5530ef0682fd95713 (boost)
http://autobuild.buildroot.net/results/af976a4805fb8b3f0c17a8e3a1f901b2255caa0b (flare-engine)
http://autobuild.buildroot.net/results/d20/d20700bd538ba1e9d45ab8a61ecbbba1a320ef38 (gst-ffmpeg)

CC: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>