SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
The STL has everything we need nowadays.
I have tried to not alter any behavior or semantics with this
change wherever possible. In particular, WriteLow and WriteHigh
in CommandProcessor retain the ability to accidentally undo
another thread's write to the upper half or lower half
respectively. If that should be fixed, it should be done in a
separate commit for clarity. One thing did change: The places
where we were using += on a volatile variable (not an atomic
operation) are now using fetch_add (actually an atomic operation).
Tested with single core and dual core on x86-64 and AArch64.
While manually capturing constexpr variables used in lambda
expressions does work, it's really easy to forget doing so since
we don't have a Windows CMake builder and the workaround isn't
necessary anywhere else. Fortunately, MSVC has a flag that fixes
the constexpr capture behavior, so let's use that instead.
Lambda expressions with uncaptured constants were leading to errors,
and there were also some warnings about deprecated functions
(QFontMetrics::width and inet_ntoa).
We need this because VS currently doesn't consider
std::is_trivially_copyable<typename
std::remove_volatile<SCPFifoStruct>::type>::value
to be true and because no compiler should consider it
to be true if we replace the volatiles with atomics.
