Changes

Revert "Introduce build script for arm-none-eabi cross-compilations"
"--enable-sanitize" does not work on jenkins build slave (debian8),
although it worked out locally for me.
Following patch will introduce corrected arm build script without
"--enable-sanitize" option:
https://gerrit.osmocom.org/#/c/2742/  
This reverts commit ba58167e1bf6ff8815c4e9e0d7b0b63ba1c529f8.
Change-Id: I644114679db1394e75ff12b0203ae8e568aff82c

Introduce build script for arm-none-eabi cross-compilations
This is a necessary step to use libosmocore-arm dep in OsmocomBB.
After this patch is submitted the "./contrib/jenkins.sh" line in 
libosmocore jenkins jobs [1][2] needs to be replaced with:
  if [[ "$JOB_NAME" == *"arch=arm-none-eabi,label=linux_amd64_debian8"*
]]
 then
   ./contrib/jenkins-arm.sh
 else
   # (FreeBSD && debian8)_amd64 builds
   ./contrib/jenkins.sh
 fi
Furthermore, the "arch" matrix-build axis has to be created, holding
"arm-none-eabi" and "amd64". Following combination filter  is necessary
to skip cross-compilations on FreeBSD buildslave:
  !(arch=="arm-none-eabi" && label=="FreeBSD_amd64")
[1] https://jenkins.osmocom.org/jenkins/job/libosmocore/
[2] https://jenkins.osmocom.org/jenkins/job/libosmocore-gerrit/
Change-Id: I0db83ad2c94ada65c00fd1bcf867830dec80085d