Clang now lowers modf/modff/modfl as builtins using the llvm.modf
intrinsic.

When expanding a load into two loads, use nuw for the add that computes
the offset from the base of the second load, because the original load
doesn't straddle the address space.

It turns out there's already a dedicated helper function for doing this,
`getObjectPtrOffset`.

This is in target-independent code, however in practice it only seems to
affact WebAssembly code, because WebAssembly load and store
instructions' constant offsets don't perform wrapping, so constant
folding often depends on the nuw flag being present.

This was noticed in the development of #119204.

The wasm backend fetches the tan runtime lib call in
`llvm/include/llvm/IR/RuntimeLibcalls.def` via `StaticLibcallNameMap()`,
but ignores the runtime function because a function sinature mapping is
not specified in RuntimeLibcallSignatureTable(). The fix is to specify
the function signatures for float32-128.

This is a fix for a build break reported on PR
https://github.com/llvm/llvm-project/pull/94559#issuecomment-2159923215.

The llvm.exp.* family of intrinsics and their corresponding libcalls
were recently added, which means we need to know their signatures.

Backwards frame index elimination uses backwards register scavenging,
which is preferred because it does not rely on accurate kill flags.

Differential Revision: https://reviews.llvm.org/D156691

The llvm.frexp.* family of intrinsics and their corresponding libcalls were
recently added, which means we need to know their signatures.

Differential Revision: https://reviews.llvm.org/D154639
Fixed: https://github.com/llvm/llvm-project/issues/63657

WebAssembly doesn't expose inexact exceptions, so frint can be mapped to
fnearbyint. Likewise, WebAssembly always rounds ties-to-even, so
froundeven can be mapped to fnearbyint.

Differential Revision: https://reviews.llvm.org/D153451

llvm.ldexp.* intrinsics were recently added to LLVM, which means
wasm now needs to know the signatures of the corresponding libcalls.

Differential Revision: https://reviews.llvm.org/D152385

Fixes: #63164

Since clang started emitting roundeven intrinsics in a7d6593a0a17, they would
cause a crash in the WebAssembly backend because it did not know the roundeven
library function signatures. Fix the crash by adding the signatures.

Differential Revision: https://reviews.llvm.org/D147476

Run update_llc_test_checks on a number of codegen tests.