The old version of boost.m4 currently included in flamerobin has an issue with gcc5 (one of its tests fails due to the first change described in https://gcc.gnu.org/gcc-5/porting_to.html , "Preprocessor issues"). This was fixed upstream in Nov 2014:
https://github.com/tsuna/boost.m4/commit/32553aaf4d5090da19aa0ec33b936982c685009f
flamerobin's boost.m4 should be updated (and the autotools stuff re-run so aclocal.m4 and configure get the change).
Boost updated https://sourceforge.net/p/flamerobin/flamerobin-git/ci/4b625c93b364eaac088a48bbc455687de204e10f/ and
aclocal and autoconf are run and i have updated the configure + aclocal.m4