nir: add nir_builder.h to the tarball

nir: add nir_builder.h to the tarball

The header was added with commit 2a135c470e3(nir: Add an ALU op builder
kind of like ir_builder.h) but did not made it into to the sources list.

Fortunately it remained unused until a recent commit faf6106c6f6(nir:
Implement a Mesa IR -> NIR translator.)

v2: Remove the bogus dependency. Tweak commit message.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>