pgsql: Honor MSVC WindowsSDKVersion if set

Honor MSVC WindowsSDKVersion if set

Add a line to the project file setting the target SDK. Otherwise, in for
example VS2017, if the default but optional 8.1 SDK is not installed the
build will fail.

Patch from Peifeng Qiu, slightly edited by me.

Discussion: /messages/by-id/CABmtVJhw1boP_bd4=b3Qv5YnqEdL696NtHFi2ruiyQ6mFHkeQQ@mail.gmail.com

Backpatch to all live branches.

Branch
------
REL9_5_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/4f435f78d536203555fbbb670f103a54f4fcbe11

Modified Files
--------------
src/tools/msvc/MSBuildProject.pm | 13 +++++++++++++
1 file changed, 13 insertions(+)