Fix `add_libclc_builtin_set` to add an appropriate dependency to either
`clspv-generate_convert.cl` or `generate_convert.cl` based on the `ARCH`
argument, rather than to both unconditionally. This fixes build failures
due to missing dependencies when `clspv*` targets are not enabled.

The added check mirrors the one from `libclc/CMakeLists.txt`.

Fixes: #127378

This commit moves the implementations of conversion builtins to the CLC
library. It keeps the dichotomy of regular vs. clspv implementations of
the conversions. However, for the sake of a consistent interface all CLC
conversion routines are built, even the ones that clspv opts out of in
the user-facing OpenCL layer.

It simultaneously updates the python script to use f-strings for
formatting.

This commit moves the sign builtin's implementation to the CLC library.
It simultaneously optimizes it (for vector types) by removing
control-flow from the implementation.

The __CLC_INTERNAL preprocessor definition has been repurposed (without
the leading underscores) to be passed when building the internal CLC
library. It was only used in one other place to guard an extra maths
preprocessor definition, which we can do unconditionally.

This removes all remaining SPIR-V workarounds for CLC functions, in an
effort to streamline the CLC implementation and prevent further issues
that #124614 had to fix. This commit fixes the same issue for the SPIR-V
targets.

Target-specific CLC implementations can and will exist, but for now
they're all identical and so the target-specific SOURCES files have been
removed. Target implementations now always include the 'generic' CLC
directory, meaning we can avoid unnecessary duplication of SOURCES
listings.

This is an external tool, so I don't think there is an expectation that
it has to be in the LLVM tools bindir. It may also be in the default
system bindir (which is not necessarily the same).

Pre-commit changes to avoid noise in an upcoming PR.

This commit moves the rotate builtin to the CLC library.

It also optimizes rotate(x, n) to generate the @llvm.fshl(x, x, n)
intrinsic, for both scalar and vector types. The previous implementation
was too cautious in its handling of the shift amount; the OpenCL rules
state that the shift amount is always treated as an unsigned value
modulo the bitwidth.

This commit moves the mad_sat builtin to the CLC library.

It also optimizes it for vector types by avoiding scalarization. To help
do this it transforms the previous control-flow code into vector select
code. This has also been done for the scalar versions for simplicity.

Symlinks are problematic on some systems. They aren't strictly necessary
as we already have build infrastructure to 'alias' multiple targets'
source directories together, as nvptx/nvptx64 has been doing.

This commit takes the opportunity to merge together the spirv and
spirv64 directories through the same system as they were identical.

Fixes #114413

This commit moves over the OpenCL clz, hadd, mad24, mad_hi, mul24,
mul_hi, popcount, rhadd, and upsample builtins to the CLC library.

This commit also optimizes the vector forms of the mul_hi and upsample
builtins to consistently remain in vector types, instead of recursively
splitting vectors down to the scalar form.

The OpenCL mad_hi builtin wasn't previously publicly available from the
CLC libraries, as it was hash-defined to mul_hi in the header files.
That issue has been fixed, and mad_hi is now exposed.

The custom AMD implementation/workaround for popcount has been removed
as it was only required for clang < 7.

There are still two integer functions which haven't been moved over. The
OpenCL mad_sat builtin uses many of the other integer builtins, and
would benefit from optimization for vector types. That can take place in
a follow-up commit. The rotate builtin could similarly use some more
dedicated focus, potentially using clang builtins.