here is the analysis of the build failures. afaics, there is only one toolchain related build failure, u-boot. Both upstream and debian already stopped building that one, and this ZUMA platform was never supported in Ubuntu 14.04 LTS.

bzr: https://launchpad.net/bugs/1451448
        regression with python 2.7.9/10

celery: https://launchpad.net/bugs/1451452
        regression (expired certificate)

cinder: https://launchpad.net/bugs/1451453
        python2.7 certificate validation

click-apparmor: https://launchpad.net/bugs/1451459
        regression with python3.4 ?

firefox: https://launchpad.net/bugs/1451453
        arm64 only, not a regression

flite: https://launchpad.net/bugs/1451462
        fails to unpack (fuzz in diff)

gcc-4.8:
        part of the proposed updates

gccgo-4.9:
        part of the proposed updates

grantlee:
        test failures on arm64

graphite2: https://launchpad.net/bugs/1451438
        no regression in test rebuild

hfsutils: https://launchpad.net/bugs/
        fails to unpack (fuzz in diff)

icu:
        fails to build in -release, built in -updates

keystone: https://launchpad.net/bugs/1451453
        python2.7 certificate validation

libarchive: https://launchpad.net/bugs/1451474
        test failures, built, when given back

libqtdbusmock: https://launchpad.net/bugs/1451474
        test failures on powerpc, fails in trusty as well

libqtdbustest: https://launchpad.net/bugs/1451474
        test failures on powerpc, fails in trusty as well

libreoffice:
        fails to build in -release, built in -updates

libxfont:
        fails to build in -release, built in -updates

lintian: https://launchpad.net/bugs/1451528
        test failure

linux:
        fails to build in -release, built in -updates

llvm-3.4:
        build failure on ppc64el, no regression

mir:
        build failure on arm64, no regression

mysql-5.5:
        fails to build in -release, built in -updates

neutron: https://launchpad.net/bugs/1451453
        python2.7 certificate validation

openjdk-7:
        fails to build in -release, built in -updates

openvpn:
        fails to build in -release, built in -updates

patch:
        fails to build in -release, built in -updates

ps3-kboot:
        build failure on arm64, no regression

openjdk-7:
        fails to build in -release, built in -updates

pygresql: https://launchpad.net/bugs/1451530
        fails to build, needs fix from utopic

python-apt: https://launchpad.net/bugs/1451531
        python 2.7.9 related?

python-django:
        fails to build in -release, built in -updates

python-docutils: https://launchpad.net/bugs/1451533
        python 2.7.9 related?

python-eventlet: https://launchpad.net/bugs/1371291
        python 2.7.9 related

python-glanceclient: https://launchpad.net/bugs/1451453
        python2.7 certificate validation

python-greenlet: https://launchpad.net/bugs/1451537
        python 2.7.9 related?

serf:
        fails to build in -release, built in -updates

spice: https://launchpad.net/bugs/1450043
        fails to apply patches

thunderbird:
        fails to build on arm64 and ppc64el, no regression.

tomcat7: https://launchpad.net/bugs/1451539
        openjdk-7 related?

usbredir: https://launchpad.net/bugs/1451540
        fails to apply patches

u-boot: https://launchpad.net/bugs/1451544
        toolchain related. Debian dropped the target, upstream too.
        see https://bugs.debian.org/754610

yaboot: https://launchpad.net/bugs/974669
        build failure, already in trusty