[Pitch] Cross-Platform C Library Access

[xwu (Xiaodi Wu)]

Pitch: The CStdlib module

I would like to pitch a new module offered by Swift by default. The module would re-export the correct module that contains the POSIX or POSIX-like C standard library for the current platform, if any; it would not be imported by default, but would allow "reasonably cross-platform" code to avoid using lengthy #if canImport(…) chains to gain access to all possible stdlibs, given that they have different names on different OSs. For example, the module may be named CStdlib. It would behave identica…