This is the first step in preparation for:
https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

This patch mostly renames files so it better reflects the function they declare.

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D155607

This is in preparation for the transition to a solution to make libc tests
hermetic with respect to their use of errno. The implementation of strdup
has been switched over to libc_errno as an example of what the code looks
like in the new way.

See #61037 for more information.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D144928

This patch adds the implementation of the custom operator new functions.
The implementation of the internal strdup has been updated to use
operator new for allocation.

We will make it a policy and document that all allocations have to go
through the libc's own operator new. A future change will also add
operator delete replacements and make it a policy that deallocations in
libc internal code have to go through those replacements.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D139584

The `strdup` family of functions rely on `malloc` to be implemented.
Its presence in the `string_utils.h` header meant that compiling many of
the string functions relied on `malloc` being implementated as well.
This patch simply moves the implementation into a new file to avoid
including `stdlib.h` from the other string functions. This was a barrier
for compiling string functions for the GPU where there is no malloc
currently.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D138607