maybe like this?

Author: picnixz

PCbuild/pythoncore.vcxproj

@@ -447,6 +447,7 @@
       <PreprocessorDefinitions>HACL_CAN_COMPILE_VEC128;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <AdditionalOptions>/arch:AVX %(AdditionalOptions)</AdditionalOptions>
     </ClCompile>
+    <ClCompile Include="..\Modules\_hashlib\hashlib_buffer.c" />
     <ClInclude Include="..\Modules\_hashlib\hashlib_buffer.h" />
     <ClInclude Include="..\Modules\_hashlib\hashlib_fetch.h" />
     <ClInclude Include="..\Modules\_hashlib\hashlib_mutex.h" />

PCbuild/pythoncore.vcxproj.filters

@@ -980,6 +980,9 @@
     <ClCompile Include="..\Modules\_hacl\Hacl_Streaming_HMAC.c">
       <Filter>Modules</Filter>
     </ClCompile>
+    <ClCompile Include="..\Modules\_hashlib\hashlib_buffer.c">
+      <Filter>Modules\_hashlib</Filter>
+    </ClCompile>
     <ClCompile Include="..\Modules\_heapqmodule.c">
       <Filter>Modules</Filter>
     </ClCompile>