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.

dmnt2: try to avoid writing out of bounds when generating packets

dmnt2: detect thread name, add monitor get mapping(s), increase buffer sizes

dmnt: enable experimental standalone usage of gdbstub, while starlink is in dev

spl: fix legacy physical keyslot compatibility

sprofile: various correctness fixes.

sprofile: fix off-by-one in struct definition, fix GetImportableProfileUrls

init: disable fsdev cwd to prevent abort on fsdev usage (fsdev should not be used)

sprof: update for 13.1.0 (format version 1)

hos: whoops

hos: better safe than sorry

hos: allow turning off ams extension hard-reqs for unit testing

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

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

lr: fix EraseRedirection hang introduced by refactoring

ams: improve offsetof style consistency

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

powctl: remove unused arm_neon header after last commit

powctl: don't require arm64 arch for floating -> fixed conversion

tipc: implement special-case templating used by 13.0.0 pgl

boot: update for 13.0.0/aula parameter changes (closes #1477)

powctl: integrate 13.0.0 changes (aula params not done yet)

strat: fix some mitm server management logic

sm/tipc: minor cleanup

strat: don't force fs globals to link into every process

sf: prevent emitting mitm/defer code unless server in process supports it

ams: allow bootloader to merely approximate correct target firmware

loader: refactor ro manager/improve accuracy

spl: refactor for accuracy/move into libstrat

os: add FlushDataCache