[windows] improve searching for MS VC runtime redistributables

[Dave Cottlehuber]

Hi,

The proposed patch adds support for the 2 most recent MS SDKs to find_redist.sh,
and a workaround to look in $ERL_TOP or $ERL_TOP/..

If there's a better approach for the workarounds please let me know;
find_redist.sh
was not intuitive for me.

git fetch git@REDACTED:dch/otp.git improved_find_redist

A+
Dave