Make mksh's mkmf.sh target-agnostic.

This isn't much, but it's a step in the right direction. Really we should
probably generate a trivial Android.mk for building the .c files used by
the mksh equivalent of a configure script.

Change-Id: I2a6d2e2b3a3ce03fea47a8ebccabd509989fbab9
Merge "Make mksh's mkmf.sh target-agnostic."