globset: use non-capture groups in regex transform

We currently implement globs by converting them to regexes, and in doing
so, sometimes use grouping. In all but one case, we used non-capturing
groups. But for alternations, we used capturing groups, which was likely
just an oversight. We don't make use of capture groups at all, and while
they usually don't have any overhead, they lead to weird cases like this
one: rust-lang/regex#1059

That particular issue is also a bug in the regex crate itself, which is
fixed in rust-lang/regex#1062. Note though that
the bug fix in the regex crate is required. Even with this patch to
globset, memory usage is reduced (by about half in rust-lang/regex#1059)
but is not returned to where it was prior to the regex 1.9 release.

crates/globset/src/glob.rs

@@ -736,7 +736,7 @@ impl Tokens {
                     // It is possible to have an empty set in which case the
                     // resulting alternation '()' would be an error.
                     if !parts.is_empty() {
-                        re.push('(');
+                        re.push_str("(?:");
                         re.push_str(&parts.join("|"));
                         re.push(')');
                     }
@@ -1276,6 +1276,7 @@ mod tests {
     toregex!(re32, "/a**", r"^/a.*.*$");
     toregex!(re33, "/**a", r"^/.*.*a$");
     toregex!(re34, "/a**b", r"^/a.*.*b$");
+    toregex!(re35, "{a,b}", r"^(?:b|a)$");
 
     matches!(match1, "a", "a");
     matches!(match2, "a*b", "a_b");