[flang] [clang] [flang][Driver] Support -pthread in the frontend (PR #77360)

[Leandro Lupori via cfe-commits]

luporl wrote:

> Could someone test this on AArch64 and/or Windows just to make sure that it passes there?

Works fine on AArch64.


https://github.com/llvm/llvm-project/pull/77360