Fix compilation on Musl systems
fstab.h is not a thing on Musl systems and thus k3b doesn't compile with it there. It seems to compile fine on FreeBSD and glibc systems only, so let's guard it for that
fstab.h is not a thing on Musl systems and thus k3b doesn't compile with it there. It seems to compile fine on FreeBSD and glibc systems only, so let's guard it for that