Stabilize the `-Csplit-debuginfo` flag...
- ...on Linux for all values of the flag. Split DWARF has been
implemented for a few months, hasn't had any bug reports and has had
some promising benchmarking for incremental debug build performance.
- ..on other platforms for the default value. It doesn't make any sense
that `-Csplit-debuginfo=packed` is unstable on Windows MSVC when
that's the default behaviour, but keep the other values unstable.
Signed-off-by: David Wood <david.wood@huawei.com>
cf2c492ef8