Make inline tcsetattr definition match constants.

Before this change we have the old NDK inline termios functions with the
modern constants. Unfortunately the old NDK inline functions relied on
hacking the constants. Fix things by sharing the implementation between
the platform and the NDK headers.

Bug: https://github.com/android-ndk/ndk/issues/441
Test: ran tests
Change-Id: I2773634059530bc954167f29c4783413a2294d5a