[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:

> Why would that even be considered a fix? You can't expect things that passed on "golden" CI at some random point to actually reliably continue working on different production setups without proper testing.

Makes sense, thanks. Updated https://github.com/llvm/llvm-project/pull/199164 to fix all tests in standalone build.

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