[clang] [llvm] [Clang] Add env var for nvptx-arch/amdgpu-arch timeout (PR #102521)

[Joel E. Denny via llvm-commits]

jdenny-ornl wrote:

FWIW, on one of my test systems that's currently very busy, check-offload consistently fails with amdgpu-arch timeouts.  However, the following so far makes it consistently succeed:

```
$ CLANG_TOOLCHAIN_PROGRAM_TIMEOUT=60 ninja check-offload
```

Previously, I've decreased lit parallelism to avoid the timeouts, but it hasn't worked consistently, and it slows down the test suite.


https://github.com/llvm/llvm-project/pull/102521