Is it possible to make `snmalloc` freestanding?

[SchrodingerZhu]

I know the build is actually free of STL linkage. However, snmalloc is not freestanding buildable because of the following:

https://github.com/microsoft/snmalloc/blob/6af38acd94d401313b7237bb7c2df5e662e135cf/src/snmalloc/ds_core/redblacktree.h#L6

Could we include the <string> header conditionally?