Minor header fixes to reduce parsing issues with Clang (#1700) ...

* Work around Clang's incomplete C++20 support for omitting typename

* vapours: fix Clang error about missing return in constexpr function

* stratosphere: fix call to non-constexpr strlen in constexpr function

strlen being constexpr is a non-compliant GCC extension; Clang
explicitly rejects it: https://reviews.llvm.org/D23692

* stratosphere: add a bunch of missing override specifiers

* stratosphere: work around Clang consteval bug

Minimal example: https://godbolt.org/z/MoM64v93M

The issue seems to be that Clang does not consider f(x) to be a
constant expression if x comes from a template argument that isn't
a non-type auto template argument (???)

We can work around this by relaxing GetMessageHeaderForCheck (by using
constexpr instead of consteval). This produces no functional changes
because the result of GetMessageHeaderForCheck() is assigned to a
constexpr variable, so the result is guaranteed to be computed
at compile-time.

* stratosphere: fix missing require clauses in definitions

GCC not requiring the require clauses to be repeated for member
definitions is actually a compiler bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96830

Clang rejects declarations with missing require clauses.

* Fix ALWAYS_INLINE_LAMBDA and parameter list relative order

While GCC doesn't seem to care about the position of the always_inline
attribute relative to the parameter list, Clang is very picky
and requires the attribute to appear after the parameter list
(and before a trailing return type)

* stratosphere: fix static constexpr member variable with incomplete type

GCC accepts this for some reason (because of the lambda?) but Clang
correctly rejects this.

ams: overhaul fs.mitm romfs ownership, bump to 1.2.4

git subrepo pull (merge) libraries ...

subrepo:
  subdir:   "libraries"
  merged:   "8764bd406"
upstream:
  origin:   "https://github.com/Atmosphere-NX/Atmosphere-libs"
  branch:   "master"
  commit:   "12d0ba172"
git-subrepo:
  version:  "0.4.1"
  origin:   "???"
  commit:   "???"

ams: bump api version to 1.2.3

ams: update for awareness of architecture revision

ams: bump version to 1.2.2

ams: bump version to 1.2.1

sprof: update for 13.1.0 (format version 1)

crypto: implement md5, which now used by sprof

kern: implement 13.1.0 kernel changes

util: add trait/macro for is_constexpr_constructible

kern/test: add wip qemu-virt board support to mesosphere

kern: optimize timespan -> tick codegen, improve .text layout

kern: avoid constexpr init for many objects (avoids unnecessary memory clear) (#1668)

kern: use new AtomicRef, use Atomic<bool>

util: better match true std::atomic semantics

kern/util: use custom atomics wrapper to substantially improve codegen

kern: update scheduler for 13.0.0 change, fix some ctz/clz bugs

ams: improve offsetof style consistency

util: improve (and use) offsetof that's """standard compliant"""

constexpr: resign ourselves to gcc dropping void -> T support

kern/util: update structure layouts to match Nintendo (saves 0x10 per KThread/KSession)

util: fix consteval CountTrailingZeroes impl

ams: bump api verrsion pre-emptively to 1.2.0

loader: refactor ro manager/improve accuracy

spl: refactor for accuracy/move into libstrat

svc: use m_ for member variables

exo/vapours: refactor member variables to m_ over this->

ams: replace most remaining operator & with std::addressof

settings: implement KeyValueStore (#1659) ...

* settings: implement KeyValueStore and dependencies

* settings: update KeyValueStore for recent refactoring

* settings: address feedback