Load libm.so via macro from gnu/lib-names.h

Hi,

we have a report in Fedora[1] - hplip generates error message in journal:

Jun 23 11:41:59 AAA perl[2750454]: common/utils.c 249: unable to load library libm.so: /lib64/libm.so: invalid ELF header

The error is fixed by the attached patch, which uses macro from lib-names.h. The macro expands to libm.so.6.

Would you mind adding the patch to HPLIP project?

Additionally, I didn't find any places where any symbols are loaded from dlopened library libm - so other possible solution is to remove whole dlopen("libm.so") blocks.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1975226