Currently Qt will download whether or not the target system supports the
package. Normally this isn't an issue since the package manager would
work out the dependencies for us, but in this case we must make sure
everything is in place before downloading the package.

This checks for the package's requirements, as well as tries to provides
hints as to what is required on some of the more cryptic dependencies.

yuzu requires CMake 3.15 yet find_program was using REQUIRED, which is
only available on 3.18 and later. Instead, we check for
"<VAR>-NOTFOUND".

In addition, check for additional requirements before building libusb or
FFmpeg with autotools. Otherwise, CMake configuration will pass yet
compilation will fail.

externals: Don't set FOUND or VERSION on LIBUSB

Fixes an issue where libusb.h wouldn't be found when building yuzu on
MSVC.

This only affects the "traditional" CMake pathway for linking libusb to
yuzu AKA MSVC. For autotools we still want to set these variables before
configuring SDL.

yuzu: main: Ensure enough space is available for RomFS dumping

Implement/Port Fastmem from Citra to Yuzu

This warns the user if there isn't enough free space to dump the entire RomFS to disk. It requires at least the size of the extracted RomFS + 1 GiB as a buffer of free space.

kernel: KLightConditionVariable: Update implementation to 12.x

This falls back to the old approach of using a virtual buffer.

Windows is untested, but this build should fix support for Windows < 10 v1803. However without fastmem support at all.

Workaround old headers and libraries shipped on MinGW.

In theory, if we have 2 MB continously mapped, this should save one layer of TLB.
Let's make it at least more likely by aligning the memory.

externals: Update SDL to 2f248a2a

cmake: Use autotools for libusb linking generally on GNU, and cleanup

Fix GCC undefined behavior sanitizer.

Updates the implementation of KLightConditionVariable to FW 12.x

hle: service: sm: Remove redundant session reservation, etc.

* Wrong alignment in u64 LOG_DEBUG -> memcpy.
* Huge shift exponent in stride calculation for linear buffer, unused result -> skipped.
* Large shift in buffer cache if word = 0, skip checking for set bits.

Non of those were critical, so this should not change any behavior.
At least with the assumption, that the last one used masking behavior, which always yield continuous_bits = 0.

- We were double-reserving, causing us to run out of sessions in Pokemon Sword & Shield.

- Pokemon Sword/Shield are still hitting this for some reason, causing an svcBreak.

hle: kernel: KServerSession: Fix client disconnected.

- Prevents us from over decrementing num_sessions.

- Prevents a cloned session's handler from being overwritten by another disconnected session.
- Fixes session handler nullptr asserts with Pokemon Sword & Shield.

ci: common: Remove 7z packaging

kernel: svc: Add missing error check to CancelSynchronization.

Use XZ instead of gzip for packing. Should save about 10 MB.

- Avoids a potential crash if the handle is invalid, and also makes this code accurate to real kernel behavior.

Removes the 7z from being package during CI, as only .tar.xz preserves
information needed on Linux, and otherwise is just extremely redundant
to package in addition to the .tar.xz.  This affects Linux releases and
PR-verify artifacts only. MSVC releases do not use this script to my
knowledge.

src/common/CMakeLists.txt: fix variable escaping