build: portability fixes ...

- Invoke Python scripts with `python3` if `python` is not available.

  Despite SciresM preferring Python 2, the scripts used in the build all
  worked in Python 3 already, so this is just a Makefile change.

- Export `MAKE` to work around a GNU bug.

  See the comment for details.

- `rmdir --ignore-fail-on-non-empty` -> `rmdir 2>/dev/null`

  macOS `rmdir` doesn't support `--ignore-fail-on-non-empty`.

  This is a slight downgrade in functionality, because now we ignore all
  errors from `rmdir` rather than just 'Directory not empty'.  I could
  have avoided this with a more complicated fix, but the benefit strikes
  me as not worth the complexity.  Let me know if you disagree.

- Append `$(DEVKITPRO)/tools/bin/` to `$PATH` when invoking
  `build_romfs`.

  This avoids the need to add devkitPro directories to `$PATH` when
  building Atmosphere.

  If you already have `build_romfs` in your PATH, then that will still
  take precedence.  (This seemed like the nicer option, though I don't
  have strong opinions.)

ams: build with -std=gnu++23

ams: support building unit test programs on windows/linux/macos

build: remove unnecessary g-dwarf4 flags

ams: update for awareness of architecture revision

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

ams-libs: move -Wno-invalid-offsetof to cxxflags, not cflags

ams-libs: use nintendo_nx identifier for source file compat bpmp<->ccplex

ams: improve offsetof style consistency

build: use DWARFv4 explicitly for IDA compatibility with debug elfs

ams: resolve source dir inconsistency

sdmmc: implement driver suitable for fs + bootloader ...

* sdmmc: begin skeletoning sdmmc driver

* sdmmc: add most of SdHostStandardController

* sdmmc: implement most of SdmmcController

* sdmmc: Sdmmc2Controller

* sdmmc: skeleton implementation of Sdmmc1Controller

* sdmmc: complete abstract logic for Sdmmc1 power controller

* sdmmc: implement gpio handling for sdmmc1-register-control

* sdmmc: implement pinmux handling for sdmmc1-register-control

* sdmmc: fix building for arm32 and in stratosphere context

* sdmmc: implement voltage enable/set for sdmmc1-register-control

* util: move T(V)SNPrintf from kernel to util

* sdmmc: implement BaseDeviceAccessor

* sdmmc: implement MmcDeviceAccessor

* sdmmc: implement clock reset controller for register api

* sdmmc: fix bug in WaitWhileCommandInhibit, add mmc accessors

* exo: add sdmmc test program

* sdmmc: fix speed mode extension, add CheckMmcConnection for debug

* sdmmc: add DeviceDetector, gpio: implement client api

* gpio: modernize client api instead of doing it the lazy way

* sdmmc: SdCardDeviceAccessor impl

* sdmmc: update test program to read first two sectors of sd card

* sdmmc: fix vref sel

* sdmmc: finish outward-facing api (untested)

* ams: changes for libvapours including tegra register defs

* sdmmc: remove hwinit

Meso build targets (#1196) ...

* meso: commit wip (thanks fincs) rewrite to support build targets

* meso: commit mostly-working build system

* meso: correct .o dependencies in kernel/kldr

* libstratosphere: fix building after PCH related build changes

Co-authored-by: fincs <fincs@devkitpro.org>

libstrat: fix building of source/os/*

ams: add support for cpu-extension specific source files

ams: update build system to add generic-fallback support

libstrat: fix bugs/compiler warnings

fs: implement AccessLog, enable for File operations

ams: add -Wno-format-truncation to flags

exo2: implement SmcGetConfig

exo2: Initial work on the exosphere rewrite. ...

exo2: Implement uncompressor stub and boot code up to Main().

exo2: implement some more init (uart/gic)

exo2: implement more of init

exo2: improve reg api, add keyslot flag setters

exo2: implement se aes decryption/enc

exo2: fix bugs in loader stub/mmu mappings

exo2: start skeletoning bootconfig/global context types

arch: fix makefile flags

exo2: implement through master key derivation

exo2: implement device master keygen

exo2: more init through start of SetupSocSecurity

exo2: implement pmc secure scratch management

se: implement sticky bit validation

libexosphere: fix building for arm32

libexo: fix makefile flags

libexo: support building for arm64/arm

sc7fw: skeleton binary

sc7fw: skeleton a little more

sc7fw: implement all non-dram functionality

exo2: fix DivideUp error

sc7fw: implement more dram code, fix reg library errors

sc7fw: complete sc7fw impl.

exo2: skeleton the rest of SetupSocSecurity

exo2: implement fiq interrupt handler

exo2: implement all exception handlers

exo2: skeleton the entire smc api, implement the svc invoker

exo2: implement rest of SetupSocSecurity

exo2: correct slave security errors

exo2: fix register definition

exo2: minor fixes

Switch atmosphere's build target to C++20. (#952) ...

* ams: update to build with gcc10/c++20

* remove mno-outline-atomics

* ams: take care of most TODO C++20s

* fusee/sept: update for gcc10

* whoosh, your code now uses pre-compiled headers

* make: dependency fixes

crypto: Implement BigNum/ExpMod

libmesosphere: precompile mesosphere.hpp

kern: switch->nx, implement sleep manager init

kern: Implement most of memory init (all cores hit main, but still more to do)

config: fix typos

kern: finish implementing assembly init routines

buildsystem: more fixes

buildsystem: avoid use of $(shell find) for significant speedup