windows: Fix Release x64 configuration

Inherit PlatformToolset from the project configuration. This allow the
project to configure PlatformToolset, and aligns the Release x64 build
with other build types.

Fixes #1430

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index e2389d5..7e91900 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -67,6 +67,9 @@
    * Remove redundant include file in timing.c. Fixes #2640 reported by irwir.
    * Fix build failure when building with mingw on Windows by including
      stdarg.h where needed. Fixes #2656.
+   * Fix Visual Studio Release x64 build configuration by inheriting
+     PlatformToolset from the project configuration. Fixes #1430 reported by
+     irwir.
 
 API Changes
    * Extend the MBEDTLS_SSL_EXPORT_KEYS to export the handshake randbytes,