fix Linux build

by default, only enable 64bit build when using ./premake4_linux64 and only 32bit build when using ./premake4_linux
remove some warning

build/premake4.lua

@@ -54,8 +54,17 @@ solution "0BulletSolution"
 		flags { "Optimize", "EnableSSE", "StaticRuntime", "NoMinimalRebuild", "FloatFast"}
 	configuration "Debug"
 		flags { "Symbols", "StaticRuntime" , "NoMinimalRebuild", "NoEditAndContinue" ,"FloatFast"}
-		
-	platforms {"x32", "x64"}
+		
+ if os.is("Linux") then
+                if os.is64bit() then
+                        platforms {"x64"}
+                else
+                        platforms {"x32"}
+                end
+        else
+                platforms {"x32", "x64"}
+        end
+
 	--platforms {"x32"}
 
   configuration {"Windows"}