I see. I agree that allowing to use embedded libtommath source is useful (it just shouldn't be default, IMHO). It was just the phrase "have problems with tommath install" which sounded as if there was some problem with building libtommath on SLE, installing it there or using it to build or run Firebird. If it was only about the absence in official repositories, that's something I cannot help with, or at least not in SLE <= 12.
On pc Debian x86-64 testing updated today, I can't build Firebird core updated today.
I used ./autogen.sh --with-builtin-tommath --with-editline=no
but building gives:
/usr/bin/ld: cannot find -ltommath
collect2: error: ld returned 1 exit status
Of course, I can install tommath but the goal is to build without installing the package and take benefit of --with-builtin-tommath