Log Message:
Instead of extracting version string from PKGNAME, use
${_EMACS_VERSION_MAJOR} and ${_EMACS_VERSION_MINOR} to determine installed
version of emacs.

Also, set minimum version of _EMACS_REQD to the same as
${_EMACS_VERSION_MAJOR}.${_EMACS_VERSION_MINOR}. Otherwise, buildlink
does not work for emacs lisp libraries.

Should fix PR/42763.