Log Message:
audio/libopenspc: Fix configure script bad grep pattern

DragonFly's modern gnu grep caught use of "[:space:]" rather than
the correct "[[:space:]]" in the Gentoo ltmain sanity check, and
returned an error breaking the configure script.  The m4 file was
correct though, so the configure wasn't really generated.  In any
case, this Gentoo error is widespread, so expect the same patch for
other packages as they are discovered.

It's possible platforms using BSD grep aren't affected.
No PKGREVISION bump required.