Fixes for Visual Studio

[sbarisic]

I updated and modified the visual studio solution file to build q3vm now. Had to include a VS specific vs_patches.h which undefines errno as it is a macro and it's used as a member of vm_t struct.

Another small issue seems to be that vm.h does not have include guards.

[codecov[bot]]

Codecov Report

Merging #3 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #3   +/-   ##
=======================================
  Coverage   91.88%   91.88%           
=======================================
  Files           2        2           
  Lines         505      505           
=======================================
  Hits          464      464           
  Misses         41       41

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[jnz]

Thank you!