Move declarations of testing-only base64 functions to their own header

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index cd68bb0..5d5b1d3 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -253,6 +253,7 @@
     <ClInclude Include="..\..\tests\include\test\drivers\signature.h" />

     <ClInclude Include="..\..\tests\include\test\drivers\size.h" />

     <ClInclude Include="..\..\tests\include\test\drivers\test_driver.h" />

+    <ClInclude Include="..\..\library\base64_invasive.h" />

     <ClInclude Include="..\..\library\check_crypto_config.h" />

     <ClInclude Include="..\..\library\common.h" />

     <ClInclude Include="..\..\library\ecp_invasive.h" />