[vm] Drop support for MSVC older than 2013

Google has required MSVC 2013 since Q2 2015, and Chromium has required
MSVC 2015 since Dec 2016. It seems safe for Dart to assume MSVC 2013.

Change-Id: I2ad2549d70b0a96085aa96e90ef15ad4c7b7acb8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107062
Reviewed-by: Régis Crelier <[email protected]>
Commit-Queue: Matthew Dempsky <[email protected]>

Author: mdempsky

runtime/platform/c99_support_win.h

@@ -77,7 +77,6 @@
 #include <sys/types.h>
 
 #if defined(_WIN32)
-#include "platform/c99_support_win.h"
 #include "platform/floating_point_win.h"
 #include "platform/inttypes_support_win.h"
 #endif  // defined(_WIN32)

runtime/platform/globals.h

@@ -15,7 +15,6 @@ platform_sources = [
   "atomic_linux.h",
   "atomic_macos.h",
   "atomic_win.h",
-  "c99_support_win.h",
   "floating_point.h",
   "floating_point_win.cc",
   "floating_point_win.h",