Fast strlen implementations (naive wide-reads, SIMD-based, and
x86_64/aarch64-optimized versions) all may perform
technically-out-of-bound reads, which leads to reports under ASan,
HWASan (on ARM machines), and also TSan (which also has the capability
to detect heap out-of-bound reads). So, we need to explicitly disable
instrumentation in all three cases.

Tragically, Clang didn't support `[[gnu::no_sanitize]]` syntax until
recently, and since we're supporting both GCC and Clang, we have to
revert to `__attribute__` syntax.

Summary:
This unifies the interface to just be a bunch of `load` and `store`
functions that optionally accept a mask / indices for gathers and
scatters with masks.

I had to rename this from `load` and `store` because it conflicts with
the other version in `op_generic`. I might just work around that with a
trait instead.

Summary:
I landed a change in clang that allows integral vectors to implicitly
convert to boolean ones. This means I can simplify the interface and
remove the need to cast to bool on every use. Also do some other
cleanups of the traits.

Summary:
Fills out some of the missing fundamental floating point operations.
These just wrap the elementwise builtin of the same name.

Summary:
This PR introduces a new 'simd.h' header that implements an interface
similar to the proposed `stdx::simd` in C++. However, we instead wrap
around the LLVM internal type. This makes heavy use of the clang vector
extensions and boolean vectors, instead using primitive vector types
instead of a class (many benefits to this).

I use this interface to implement a generic strlen implementation, but
propse we use this for math. Right now this requires a feature only
introduced in clang-22.

Followup to #127523

There were some test failures on arm32 after enabling Wconversion. There
were some tests that were failing due to missing casts. Also I changed
BigInt's `safe_get_at` back to being signed since it needed the ability
to be negative.

Fixed imports for all files *within* `libc/src/string/memory_utils`.
Note: This doesn't include **all** files that need to be fixed.

Fixes #86579

The patch primarily cleans up some incorrect includes. The `LIBC_INLINE`
macro is defined in `attributes.h`, not `config.h`. There appears to be
no need to change the CMake and Bazel build files.

This is a part of #97655.

Reverts llvm/llvm-project#98075

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