installer: copy `node.d` only with node_use_dtrace

tools/install.py

@@ -129,9 +129,7 @@ def subdir_files(path, dest, action):
 def files(action):
   action(['out/Release/node'], 'bin/node')
 
-  # install unconditionally, checking if the platform supports dtrace doesn't
-  # work when cross-compiling and besides, there's at least one linux flavor
-  # with dtrace support now (oracle's "unbreakable" linux)
+  if 'true' == variables.get('node_use_dtrace'):
     action(['out/Release/node.d'], 'lib/dtrace/node.d')
 
   if 'freebsd' in sys.platform or 'openbsd' in sys.platform: