Each file dump now starts with a `; ---` comment and ends with a blank
line. This makes it easier to visually scan the dump for a file of
interest. The comment format is somewhat arbitrary; I chose `---` to
align with the `--- filename.carbon` separator in SemIR dumps, but
without the filename, because that appears on each of the next two lines
already.
This extends #6364 to allow having:
* `Cpp.unsigned_long` as a distinct type when `unsigned long` is 32
bits.
* `Cpp.long_long` and `Cpp.unsigned_long_long` as distinct types when
`long` and `unsigned long` are 64 bits.
Similarly to #6364, we only support implicit conversions from the
matching literal type (`u32`, `i64` and `u64`).
See #6275 for rationale.
Part of #5263.
Geoff Romer
David Blaikie
Dana Jansens
Boaz Brickner