Getting error while make x11iraf in ubuntu 20.04

[BOOM5s]

Warning, mkpkg line 13: module libpkg.a' not found or returned error
xc -c -x x_ism.x
envinit: cannot open iraf$extern/.zzsetenv.def' envinit: cannot open iraf$extern/.zzsetenv.def'
x_ism.x:13:10: fatal error: f2c.h: No such file or directory
compilation terminated.
xc -Nz -z x_ism.o libpkg.a -o ism_wcspix.e -lds -lxtools -liminterp -lslalib
envinit: cannot open iraf$extern/.zzsetenv.def' Warning: file x_ism.o' not found
Warning: file libpkg.a' not found gcc: error: libmain.o: No such file or directory gcc: error: libex.a: No such file or directory gcc: error: liblapack.a: No such file or directory gcc: error: libsys.a: No such file or directory gcc: error: libvops.a: No such file or directory gcc: error: libVOTable.a: No such file or directory Warning, mkpkg line 3: module relink' not found or returned error `

[olebole]

The error message means that the build didn't find your IRAF installation (f.e. if the iraf environment variable was not set).
As long as you don't neet ximtool or can live without WCS support in ximtool, you can ignore this. xgterm is already built and can be used (just copy it to your PATH).
For Ubuntu 20.04, there are also pre-built packages: xgterm and ximtool. Using these makes them updateable when you migrate to a more modern version.