W32 VS projects: use C17 if available

w32/common/common-build-settings.vcxproj

@@ -32,6 +32,7 @@
       <TreatSpecificWarningsAsErrors>4013</TreatSpecificWarningsAsErrors>
       <ProgramDataBaseFileName>$(IntDir)$(TargetName).pdb</ProgramDataBaseFileName>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
+      <LanguageStandard_C Condition="'%(ClCompile.LanguageStandard_C)' != ''">stdc17</LanguageStandard_C>
     </ClCompile>
     <Link>
       <GenerateDebugInformation>true</GenerateDebugInformation>