Added windows platform support to premake (google#567)

* Added windows platform support to premake

Win32 and Win64 configuration support for visual studio solutions

* Update premake5.lua

Fixed platform support for linux, made x64 default

* Update premake5.lua

Fix typo

Author: tavrez

premake5.lua

@@ -1,6 +1,7 @@
 -- A solution contains projects, and defines the available configurations
 solution "brotli"
 configurations { "Release", "Debug" }
+platforms { "x64", "x86" }
 targetdir "bin"
 location "buildfiles"
 flags "RelativeLinks"
@@ -13,6 +14,12 @@ filter "configurations:Release"
 filter "configurations:Debug"
   flags { "Symbols" }
 
+filter { "platforms:x64" }
+   architecture "x86_64"
+
+filter { "platforms:x86" }
+   architecture "x86"
+
 configuration { "gmake" }
   buildoptions { "-Wall -fno-omit-frame-pointer" }
   location "buildfiles/gmake"