Only build OB-Valve binaries on Mac OS X for now (bug 4392, r=dvander).

extensions/sdktools/AMBuilder

@@ -2,6 +2,10 @@
 import os
 
 for i in SM.sdkInfo:
+	sdk = SM.sdkInfo[i]
+	if AMBuild.target['platform'] not in sdk['platform']:
+		continue
+
 	compiler = SM.DefaultHL2Compiler('extensions/sdktools', i)
 	compiler['CXXINCLUDES'].append(os.path.join(AMBuild.sourceFolder, 'public', 'jit'))
 	compiler['CXXINCLUDES'].append(os.path.join(AMBuild.sourceFolder, 'public', 'jit', 'x86'))
@@ -9,7 +13,6 @@ for i in SM.sdkInfo:
 	if i != 'ep1':
 		compiler['CDEFINES'].append('HOOKING_ENABLED')
 
-	sdk = SM.sdkInfo[i]
 	name = 'sdktools.ext.' + sdk['ext']
 	extension = AMBuild.AddJob(name)
 	binary = Cpp.LibraryBuilder(name, AMBuild, extension, compiler)