Add a patch files for stable/12 r342281, which corresponds to the
following upstream revision:

https://reviews.llvm.org/rL329671

This fixes 'Assertion failed: (Result.isUninit() && "temporary created
multiple times"), function createTemporary' errors (if assertions are
enabled, otherwise the compiler internal state might go bad), when
building the graphics/rawtherapee port.

Submitted by: dim
Differential Revision: https://reviews.freebsd.org/D18699