android: reduce memory consumption by gradle builds

platforms/android/build_sdk.py

@@ -231,7 +231,10 @@ class Builder:
         cmd += [ "-D%s='%s'" % (k, v) for (k, v) in cmake_vars.items() if v is not None]
         cmd.append(self.opencvdir)
         execute(cmd)
-        execute([self.ninja_path, "install" if self.debug else "install/strip"])
+        # full parallelism for C++ compilation tasks
+        execute([self.ninja_path, "opencv_modules"])
+        # limit parallelism for Gradle steps (avoid huge memory consumption)
+        execute([self.ninja_path, '-j3', "install" if self.debug else "install/strip"])
 
     def build_javadoc(self):
         classpaths = []