Simplify the code around the call to gen_main_file

There's no need to keep the directory lists separated until the last
minute.

No semantic change. The generated files change slightly because there
was one directory list where slashes were not changed to backslashes
like in the other five. This does not affect their semantics.
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index 0e40e35..eb5f275 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -222,13 +222,13 @@
     <ClInclude Include="..\..\include\psa\crypto_struct.h" />

     <ClInclude Include="..\..\include\psa\crypto_types.h" />

     <ClInclude Include="..\..\include\psa\crypto_values.h" />

-    <ClInclude Include="..\..\library/psa_crypto_core.h" />

-    <ClInclude Include="..\..\library/psa_crypto_invasive.h" />

-    <ClInclude Include="..\..\library/psa_crypto_its.h" />

-    <ClInclude Include="..\..\library/psa_crypto_se.h" />

-    <ClInclude Include="..\..\library/psa_crypto_service_integration.h" />

-    <ClInclude Include="..\..\library/psa_crypto_slot_management.h" />

-    <ClInclude Include="..\..\library/psa_crypto_storage.h" />

+    <ClInclude Include="..\..\library\psa_crypto_core.h" />

+    <ClInclude Include="..\..\library\psa_crypto_invasive.h" />

+    <ClInclude Include="..\..\library\psa_crypto_its.h" />

+    <ClInclude Include="..\..\library\psa_crypto_se.h" />

+    <ClInclude Include="..\..\library\psa_crypto_service_integration.h" />

+    <ClInclude Include="..\..\library\psa_crypto_slot_management.h" />

+    <ClInclude Include="..\..\library\psa_crypto_storage.h" />

     <ClInclude Include="..\..\3rdparty\everest\include\everest\everest.h" />

     <ClInclude Include="..\..\3rdparty\everest\include\everest\Hacl_Curve25519.h" />

     <ClInclude Include="..\..\3rdparty\everest\include\everest\kremlib.h" />