Add an error message if android NDK is not installed

Author: ArchLinus

tools/android.py

@@ -64,6 +64,12 @@ def generate(env):
  elif sys.platform == "darwin":
  toolchain += "darwin-x86_64"
  env.Append(LINKFLAGS=["-shared"])
+
+ if not os.path.exists(toolchain):
+ print("ERROR: Could not find NDK toolchain at " + toolchain + ".") 
+ print("Make sure NDK version " + get_ndk_version() + " is installed.")
+ env.Exit(1)
+
  env.PrependENVPath("PATH", toolchain + "/bin") # This does nothing half of the time, but we'll put it here anyways
 
  # Get architecture info