Fix a possible race condition affecting parallel builds configured with

``--enable-experimental-jit``, in which compilation errors could be caused

by an incompletely-generated header file.

):

stencil_groups=asyncio.run(self._build_stencils())

withjit_stencils.open("w")asfile:

file.write(digest)

ifcomment:

file.write(f"//{comment}\n\n")

file.write("")

forlinein_writer.dump(stencil_groups):

file.write(f"{line}\n")

try:

withjit_stencils_new.open("w")asfile:

file.write(digest)

ifcomment:

file.write(f"//{comment}\n")

file.write("\n")

forlinein_writer.dump(stencil_groups):

file.write(f"{line}\n")

jit_stencils_new.replace(jit_stencils)

finally:

jit_stencils_new.unlink(missing_ok=True)

class_COFF(