strdup_compat.h: re-spin this compat header ; use math_compat.h as template

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

json-c.vcxproj

@@ -151,6 +151,7 @@ copy json_config.h.win32 json_config.h
     <ClInclude Include="json_util.h" />
     <ClInclude Include="linkhash.h" />
     <ClInclude Include="math_compat.h" />
+    <ClInclude Include="strdup_compat.h" />
     <ClInclude Include="printbuf.h" />
     <ClInclude Include="random_seed.h" />
   </ItemGroup>
@@ -164,4 +165,4 @@ copy json_config.h.win32 json_config.h
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>