amrwbenc: Prefix a few more symbols

This avoids clashes between symbols in amrwbenc and amrwb, if they
are linked into the same module.

Change-Id: I1d26b35403ae1bc5a69fe4cf490abbc03286cb29
amrwbenc/aacenc: Look for voMem.h in the local directory, too

This helps using the headers without further modifications, if
they are installed into a subdirectory.

Change-Id: I95b59cc5a37972df49b84fb066071e7a892bb412
aacenc: Prefix more symbols

This avoids symbol clashes, if linking this code into the same
module as the libfaac library.

Change-Id: Ia29a99351b886d57448775be4d8891268f562d14
aacenc: basic_op: use 32-bit types

Using 16-bit types unnecessarily results in numerous extra sign/zero
extend operations even when the value is known to fit in 16 bits.

Change-Id: If970aad29d5b3fe4f62ce9d285f1d0b8eacbd43c