Add -Wno-unused-parameter to LOCAL_CFLAGS

Some JNI functions ignore the JNI environment and class information, but
still take the parameters -- causing a build failure with clang (and gcc
with -Wextra enabled). Ignore this.

Change-Id: I049fcf65991b19d2416fce105699311803b43cfc
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>