[compiler-rt] [compiler-rt] Simplify and rename of operator_new_size_type (PR #83912)

[via llvm-commits]

zmodem wrote:

This broke building with MSVC for 32-bit x86: #101998. Can we revert it? It still seems to revert cleanly, and I can't really think of a better fix than putting the old `operator_new_size_type` back.

https://github.com/llvm/llvm-project/pull/83912