SVE/SVE2 is a new SIMD extension for AArch64. Compared to NEON, SVE/SVE2 brings the following benefits that are good for SDL projects:
- Lane prediction: we don't have to treat the tail part of a stride separately when the width is n times the hardware vector size
- Although the performance is almost no difference from NEON when the hardware vector size is 128bits, when the hardware provides a longer vector size, e.g. 256, 512, ... 2048, we can enjoy the large performance gain without modifying the source code or recompiling a library.
The functional correctness is validated in a dedicated [qemu project](https://github.com/GorgonMeducer/aarch64_qemu_mac_template/tree/SDL-SVE2-Acceleration-Validation).
The performance is tested on [Radxa Orion 6 N](https://radxa.com/products/orion/o6n/), which provides 4x A720 and 4x A520 processors. Since the vector size is 128 bits, which is the same as NEON, the performance is almost the same (or no worse than) the NEON acceleration.
Everything in SDL3 up to the ABI lock is reported as available since 3.1.3.
Everything else will be reported as since 3.2.0 (what will be the first
official release).
Also ran a Perl script over the headers to change everything to 3.1.3 that
wasn't an API function, since fnsince.pl can't manage those. If there's a
macro or datatype that has snuck in that needs to be 3.2.0 instead, we'll
have to manually fix it up, but it shouldn't be a big deal in any case.
Reference PR #11304.
We require stdbool.h in the build environment, so we might as well use the plain bool type.
If your environment doesn't have stdbool.h, this simple replacement will suffice:
typedef signed char bool;
This was the only API that broke the "GetNumThings" convention
used elsewhere, so renaming it helps with consistency.
Adding "logical cores" to the name also makes it a bit
more immediately obvious what the count actually represents.
I ran this script in the include directory:
```sh
sed -i '' -e 's,#include "\(SDL.*\)",#include <SDL3/\1>,' *.h
```
I ran this script in the src directory:
```sh
for i in ../include/SDL3/SDL*.h
do hdr=$(basename $i)
if [ x"$(echo $hdr | egrep 'SDL_main|SDL_name|SDL_test|SDL_syswm|SDL_opengl|SDL_egl|SDL_vulkan')" != x ]; then
find . -type f -exec sed -i '' -e 's,#include "\('$hdr'\)",#include <SDL3/\1>,' {} \;
else
find . -type f -exec sed -i '' -e '/#include "'$hdr'"/d' {} \;
fi
done
```
Fixes https://github.com/libsdl-org/SDL/issues/6575
