Move MCR from PERL to PERLRUN on VMS.

And other *RUN variables.  Since on VMS you can't just supply an
executable file on the command line (well, unless it's on DCL$PATH),
but need to prepend MCR to it, we've always had PERL as a command
rather than just a filename.

But since b4de841e328911 we now have the assumption that the first
space-delimited chunk of PERL is a filename and anything after one
or more spaces are flags that can be separated out.

So move the MCR to the variables that are actually used to run
perl; I don't think think these existed when the MCR logic was
initially added, so that explains why the MCR was always in PERL.
Quotes are not stripped from argv[0] on VMS.

So we have to strip them ourselves in order to avoid a parsing
error that looks like:

$ mcr "[]miniperl.exe" -v
%DCL-W-ACTIMAGE, error activating image "[]miniperl.exe"
-CLI-E-IMGNAME, image file DSA0:"[]MINIPERL.EXE".;
-RMS-F-FNM, error in file name
Avoid .NOTPARALLEL on VMS.

It's a syntax error with MMS and MMK.