Instead require `1e9` and `0x1p9`, disallowing the trailing dot.
This change to the grammar is consistent with forbidding `1.` and `0x1.`
as float literals and ensures there is only one way to do things here.
The `1 - shift` expression was computed using small unsigned types and
then casted to i32, producing either an underflow error or an incorrect
result.
Reported by `@notviri` in #8733
These were never working with native CPU features. In this branch,
we fix native CPU features not being enabled on Windows, and regress
f128 language features. In the llvm10 branch, all this is fixed,
and the tests are re-enabled.
