[libclc] [libclc] Move external-funcs.test to static file and use IR checks for .cl tests (PR #197151)

[Wenju He via cfe-commits]

wenju-he wrote:

> Looks like it's not telling clang where `libclc.bc` is (presumably via overriding `-resource-dir`).

There is a `--libclc-lib` flag to override. Disabling .cl tests in standalone build is simpler fix: https://github.com/llvm/llvm-project/pull/199164
Tt is probably enough to just test them in in-tree build.

https://github.com/llvm/llvm-project/pull/197151