[libc++] Simplify how the global stream tests are written (#66842)

Instead of relying on Bash, use the builtin Lit commands whenever
possible. The motivation is to stop running %t.exe behind Bash, which
breaks on macOS 13.5 with SIP enabled because DYLD_LIBRARY_PATH isn't
forwarded to the underlying process when running through a protected
process.

For more details, see [1].

[1]: https://developer.apple.com/library/archive/documentation/Security/Conceptual/System_Integrity_Protection_Guide/RuntimeProtections/RuntimeProtections.html