I can build it just fine on its own. But not when building it using an ebuild. These are sandboxed builds (analogous to *.src.rpm packages on RPM-based distros.) fizmo's build system seems to ignore many variables and have some of them hardcoded (like CFLAGS and LDFLAGS). These issues have been somewhat worked around already by David Leverton, who maintains fizmo in the interactive-fiction Gentoo overlay. But building fails with:
"x86_64-pc-linux-gnu-gcc" -pipe -mtune=native -march=native -O2 -fomit-frame-pointer -floop-interchange -floop-strip-mine -floop-block -Wall -Wextra -DENABLE_READCHAR_VIA_TERMIOS= -I/usr/include/libxml2 -I/var/tmp/portage/games-engines/fizmo-0.7.2/work/fizmo-0.7.2/build/include/fizmo -c fizmo-console.c
"x86_64-pc-linux-gnu-gcc" -Wl,--as-needed -Wl,-O1 -Wl,--hash-style=gnu -Wl,--sort-common fizmo-console.o -o fizmo-console -lm -L/var/tmp/portage/games-engines/fizmo-0.7.2/work/fizmo-0.7.2/build/lib/fizmo -lfizmo -lxml2
/usr/lib/gcc/x86_64-pc-linux-gnu/4.7.1/../../../../x86_64-pc-linux-gnu/bin/ld: /var/tmp/portage/games-engines/fizmo-0.7.2/work/fizmo-0.7.2/build/lib/fizmo/libfizmo.a(math.o): undefined reference to symbol 'rint@@GLIBC_2.2.5'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.7.1/../../../../x86_64-pc-linux-gnu/bin/ld: note: 'rint@@GLIBC_2.2.5' is defined in DSO /usr/lib/gcc/x86_64-pc-linux-gnu/4.7.1/../../../../lib64/libm.so so try adding it to the linker command line
/usr/lib/gcc/x86_64-pc-linux-gnu/4.7.1/../../../../lib64/libm.so: could not read symbols: Invalid operation
I tried for quite a bit to find out what's causing this, but failed and gave up.