Build system tweaks for Valgrind.

Added LOCAL_NO_CRT to enable building executables that do not link
to the C runtime library.

Removed support for LOCAL_MODULE_SUBDIR since it was broken
and unused.  (Was going to use it but ended up using LOCAL_MODULE_PATH
instead.)

Change-Id: Ifed4ffe17003d90370c711ea6606e2b75e841dee