[clang] [PS4, PS5][Driver] Detangle --sysroot and -isysroot (PR #107410)

[Edd Dawson via cfe-commits]

playstation-edd wrote:

> According to [gcc docs](https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html) `--sysroot` applies to headers and libraries, and `-isysroot` overrides it for headers only. This is different from the "independence" described for World 2. That is, if we have only `--sysroot` it should apply to both.

I'm not sure what resource is (mis)read to come to the conclusion that world 2 was normal. Thanks for checking!

I have pushed an update which has `--sysroot` apply to both header and libraries, unless both `--sysroot` and `-isysroot` are supplied, win which case the former applies to libraries and the latter to headers.


https://github.com/llvm/llvm-project/pull/107410