Fix untidinesses in compile.el.

* lisp/progmodes/compile.el (compilation--margin-string): Renamed from
compilation-margin-string.  Use defconst rather than defvar.  Use propertize
rather than a separate put-text-property.  Trim the doc string.
1 job for master in 57 minutes and 56 seconds (queued for 3 seconds)
Status Job ID Name Coverage
failed #3232


Name Stage Failure
test-all Test
Makefile:319: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1