The names stdout / stderr are bound to conflict with existing
declarations when compiling against other LibC's. The build on OpenBSD
is broken for this reason at the moment.
Lets rename the members to more generic names to resolve the situation.
Previously, Core::command only returned a String which contained the
data from stdout.
The CommandResult struct contains the exit code as well as the data
from stdout and stderr.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
