Looks like someone renamed (or something) md5c.c to md5.c.
diff --git a/PCbuild/pythoncore.vcproj b/PCbuild/pythoncore.vcproj
index 2ead78a..3bd740f 100644
--- a/PCbuild/pythoncore.vcproj
+++ b/PCbuild/pythoncore.vcproj
@@ -623,7 +623,7 @@
 			RelativePath="..\Modules\mathmodule.c">
 		</File>
 		<File
-			RelativePath="..\Modules\md5c.c">
+			RelativePath="..\Modules\md5.c">
 		</File>
 		<File
 			RelativePath="..\Modules\md5module.c">