build: allow correct tools to be used for dmg creation.

These come from the enironment, which will be properly setup by Make with
the paths gleaned from configure.
Also don't crash if plugins are static.

contrib/macdeploy/macdeployqtplus

@@ -196,7 +196,8 @@ class DeploymentInfo(object):
 def getFrameworks(binaryPath, verbose):
     if verbose >= 3:
         print "Inspecting with otool: " + binaryPath
-    otool = subprocess.Popen(["otool", "-L", binaryPath], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    otoolbin=os.getenv("OTOOL", "otool")
+    otool = subprocess.Popen([otoolbin, "-L", binaryPath], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     o_stdout, o_stderr = otool.communicate()
     if otool.returncode != 0:
         if verbose >= 1:
@@ -221,7 +222,8 @@ def getFrameworks(binaryPath, verbose):
     return libraries
 
 def runInstallNameTool(action, *args):
-    subprocess.check_call(["install_name_tool", "-"+action] + list(args))
+    installnametoolbin=os.getenv("INSTALLNAMETOOL", "install_name_tool")
+    subprocess.check_call([installnametoolbin, "-"+action] + list(args))
 
 def changeInstallName(oldName, newName, binaryPath, verbose):
     if verbose >= 3:
@@ -239,10 +241,11 @@ def changeIdentification(id, binaryPath, verbose):
     runInstallNameTool("id", id, binaryPath)
 
 def runStrip(binaryPath, verbose):
+    stripbin=os.getenv("STRIP", "strip")
     if verbose >= 3:
         print "Using strip:"
         print " stripped", binaryPath
-    subprocess.check_call(["strip", "-x", binaryPath])
+    subprocess.check_call([stripbin, "-x", binaryPath])
 
 def copyFramework(framework, path, verbose):
     if framework.sourceFilePath.startswith("Qt"):
@@ -347,6 +350,8 @@ def deployFrameworksForAppBundle(applicationBundle, strip, verbose):
 def deployPlugins(appBundleInfo, deploymentInfo, strip, verbose):
     # Lookup available plugins, exclude unneeded
     plugins = []
+    if deploymentInfo.pluginPath is None:
+        return
     for dirpath, dirnames, filenames in os.walk(deploymentInfo.pluginPath):
         pluginDirectory = os.path.relpath(dirpath, deploymentInfo.pluginPath)
         if pluginDirectory == "designer":