* lisp/progmodes/gdb-mi.el: Avoid backtracking in regexp matcher.

* lisp/progmodes/gdb-mi.el: Avoid backtracking in regexp matcher.
(gdb--string-regexp): New constant.
(gdb-tooltip-print, gdb-var-evaluate-expression-handler)
(gdbmi-bnf-stream-record, gdb-jsonify-buffer): Use it.
(gdb-source-file-regexp, gdb-prompt-name-regexp): Use it and change
submatch 1.
(gdb-get-source-file-list, gdb-get-prompt, gdb-get-source-file):
Adjust use accordingly.
(gdb-breakpoints-list-handler-custom): Pre-build the y/n string.