cmd/vet: detect regexp.MustCompile guaranteed to fail

[rsc]

regexp.MustCompile(literal-regexp) could be checked by vet to make sure the regexp
really does compile.

[dsymonds]

Comment 1:

Other Dave was going to take a crack at this.

Labels changed: added repo-tools.

Owner changed to @okdave.

[ianlancetaylor]

Comment 2:

Might as well check regexp.Compile with a string literal while you're at it--a bad
regexp there is worth a warning too.

[dsymonds]

Comment 3:

It was decided not to do this.
https://golang.org/cl/98850043/

Status changed to WontFix.