In 32-bit build with --enable-shared, there is a lot of
register pressure and register src_strideq is reused.
The code needs to use the stack based version of src_stride,
but this doesn't compile when used in an lea instruction.

This patch also fixes a related segmentation fault caused by the
implementation using src_strideq even though it has been
reused.

This patch also fixes the HBD subpel variance tests that fail
when compiled without disable-optimizations.
These failures were caused by local variables in the assembler
routines colliding with the caller's stack frame.

Change-Id: Ice9d4dafdcbdc6038ad5ee7c1c09a8f06deca362