conftest.c: command not found
solved downstream with another configure.ac fix, see https://bugs.gentoo.org/show_bug.cgi?id=949813
the problem shows when building with --disable-gui
the package is configured as ./configure --prefix=/usr --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib --datarootdir=/usr/share --disable-dependency-tracking --disable-silent-rules --disable-static --docdir=/usr/share/doc/gpsim-9999 --htmldir=/usr/share/doc/gpsim-9999/html --with-sysroot=/ --libdir=/usr/lib64 --disable-static --disable-gui
segfault at startup
external system KLU library
The core part of the patch, i.e. the modification of configure.ac, is like the one I suggested so that solves the problem here.
Here I am using libfpx 1.3.1 with gcc-12.3.1