swr: automake: don't ship LLVM version specific generated sources

swr: automake: don't ship LLVM version specific generated sources

Otherwise things will fail to build, if the builder is using another
version of LLVM.

v2: annotate all the dependencies of builder_gen.h
v3: clean the generated files as needed
v4: comment cleanups (Tim)

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Tested-by: Tim Rowley <timothy.o.rowley@intel.com>
Tested-by: Chuck Atkins <chuck.atkins@kitware.com> (v2)
Reported-by: Chuck Atkins <chuck.atkins@kitware.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>