Default to 64-bit MSVC toolchain

Prevents linking issues with LLVM 7.0.

Bug b/115344057

Change-Id: I7270c2bcf6095b1ec9911074b3119f87680a7cad
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28168
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Reactor/Reactor.vcxproj

diff --git a/src/Reactor/Reactor.vcxproj b/src/Reactor/Reactor.vcxproj
index 60c15c5..7e01bc5 100644
--- a/src/Reactor/Reactor.vcxproj
+++ b/src/Reactor/Reactor.vcxproj
@@ -31,6 +31,7 @@
     <RootNamespace>Reactor</RootNamespace>

     <Keyword>Win32Proj</Keyword>

     <WindowsTargetPlatformVersion>10.0.16299.0</WindowsTargetPlatformVersion>

+    <PreferredToolArchitecture>x64</PreferredToolArchitecture>

   </PropertyGroup>

   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />

   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">