gnu: gcc-mesboot-wrapper: Fix 'version' field.

Until now the 'version' field would match
'gcc-mesboot1-wrapper' ("4.7.4") instead of that of
'gcc-mesboot' ("4.9.4").

* gnu/packages/commencement.scm (gcc-mesboot-wrapper)[version]: New
field.

gnu/packages/commencement.scm

@@ -1350,6 +1350,7 @@ exec " gcc "/bin/" program
    (package
      (inherit gcc-mesboot1-wrapper)
      (name "gcc-mesboot-wrapper")
+     (version (package-version gcc-mesboot))
      (source #f)
      (inputs '())
      (native-inputs `(("bash" ,%bootstrap-coreutils&co)