migrate to use arm-none-eabi build of libosmocore.git
We currently have some partial copied hack of libosmocore inside simtrace2.git, which is of course a bad idea.
Instead, we should use a libosmocore from libosmocore.git which was built + installed using
./configure --enable-static --prefix=/usr/local/arm-none-eabi --host=arm-none-eabi --enable-embedded CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs -Werror"
This library can then be used by a variety of embedded/firmware builds, such as OsmocomBB and others.