When linking with cmake and vs_link_* the command line
could be too long for cmd.exe, which needs not to be
called in this case. (was not cached by a test)
Introduce rules which don't use the shell and use this
rule when there are no pre or post step.
For free we get a small speedup, because cmd is then
not called.
Also be more accurate when estimating the
command line length.
When MinGW is used slashes are used for dependencies
because ar.exe can't read rsp files with backslashes.
Many thx to Claus Klein for starting working on this.
Peter Kuemmel
Brad King
Peter Collingbourne