Support extra-verbose builds

[comex]

• The bootstrap crate currently passes -v to Cargo if itself invoked with -vv. But Cargo supports -vv (to show build script output), so make bootstrap pass that if itself invoked with -vvv. (More specifically, pass N '-v's to Cargo if invoked with N+1 of them.)

• bootstrap.py currently tries to pass on up to two '-v's to cargo when building bootstrap, but incorrectly ('-v' is marked as 'store_true', so argparse stores either False or True, ignoring multiple '-v's). Fix this, allow passing any number of '-v's, and make it consistent with bootstrap's invocation of Cargo (i.e. subtract one from the number of '-v's).

• Also improve bootstrap.py's config.toml 'parsing' to support arbitrary verbosity levels, + allow command line to override it.

[emilyalbini]

Highfive failed to assign a reviewer.

r? @Mark-Simulacrum

[Mark-Simulacrum]

r=me after fixing tidy:

[00:06:25] tidy error: /checkout/src/bootstrap/flags.rs:32: line longer than 100 chars

[kennytm]

In both Python 2 and 3, range(0, self.verbose - 1) will be empty when self.verbose - 1 is zero or negative, so the max(0, _) is unnecessary.

[kennytm]

🤣

(This line is >100 chars BTW)

[kennytm]

This can be simply self.verbosity.saturating_sub(1)

Alternatively you could use this in src/bootstrap/builder.rs to entirely get rid of this function.

// if rustbuild is invoked with N `-v`s, we pass N-1 `-v`s to cargo.for _ in1..self.verbosity{
cargo.arg("-v");}

[comex]

Updated in light of review comments.

[Mark-Simulacrum]

r? @kennytm

[kennytm]

@bors r+

[bors]

📌 Commit ec49234 has been approved by kennytm

[alexcrichton]

@bors: rollup