glob: Add an extra glob pattern compilation stage.

glob: Add an extra glob pattern compilation stage.

* guix/glob.scm (compile-glob-pattern): Rename to...
(string->sglob): ... this.
(compile-sglob, string->compiled-sglob): New procedures.
(glob-match?): Replace '?, 'range, and 'set with a single clause.
* tests/glob.scm (test-compile-glob-pattern): Rename to...
(test-string->sglob): ... this.  Adjust accordingly.
(test-glob-match): Use 'string->compiled-sglob' instead of
'compile-glob-pattern'.
* gnu/build/linux-modules.scm (read-module-aliases): Use
'string->compiled-sglob' instead of 'compile-glob-pattern'.