- Use svec instead of tuple for arguments (better match for ABI which
   will require boxes)
 - Directly forward single svec argument, both runtime and codegen,
   without copying.
 - Optimize all consistant builtin functions of constant arguments, not
   just ones with special tfuncs. Reducing code duplication and
   divergence.
 - Codegen for `svec()` directly, so optimizer can see each store (and
   doesn't have to build the whole thing on the stack first).

Without a release store, it seems LLVM considers it a data race to have
read the initial state on another thread. Marking this as a release
store seems sufficient to prevent that optimization. It is also more
consistent with how we initialize and write to most other structs,
particularly since #55767.

Fixes #59547 (more)

…59548)

- Use svec instead of tuple for arguments (better match for ABI which
will require boxes)
- Directly forward single svec argument, both runtime and codegen,
without copying.
- Optimize all consistant builtin functions of constant arguments, not
just ones with special tfuncs. Reducing code duplication and divergence.
- Codegen for `svec()` directly, so optimizer can see each store (and
doesn't have to build the whole thing on the stack first).

Written with help by Claude

This makes math.jl slightly simpler with no functional differences.

While cleaning up, I also removed Base.Math.libm which appears to be
completely unused (and is an alias to Base.libm_name)

…59506)

`Base` code often assumes that a constructor will return a value of the
stated type. This is false, cross-reference issue #42372.

This change prevents several stack overflows that arise when a generic
method is called with a newly-defined type with such a weird constructor
for some `Base`-defined type.