Specify clang as the toolset for the rive project

Rive doesn't build in Visual Studio with the MSVC toolset.

build/premake5.lua

diff --git a/build/premake5.lua b/build/premake5.lua
index f6c1c32..4d0c8db 100644
--- a/build/premake5.lua
+++ b/build/premake5.lua
@@ -5,6 +5,7 @@
     kind "StaticLib"
     language "C++"
     cppdialect "C++17"
+    toolset "clang"
     targetdir "%{cfg.system}/bin/%{cfg.buildcfg}"
     objdir "%{cfg.system}/obj/%{cfg.buildcfg}"
     includedirs {"../include"}
@@ -78,4 +79,4 @@
         { "arm64" }
     }
 
-}
\ No newline at end of file
+}