clang/llvm: fix version detection (#19978)

This PR fixes two problems with clang/llvm's version detection. clang's
version output looks like this:

```
clang version 11.0.0
Target: x86_64-unknown-linux-gnu
```

This caused clang's version to be misdetected as:

```
clang@11.0.0
Target:
```

This resulted in errors when trying to actually use it as a compiler.

When using `spack external find`, we couldn't determine the compiler
version, resulting in errors like this:

```
==> Warning: "llvm@11.0.0+clang+lld+lldb" has been detected on the system but will not be added to packages.yaml [reason=c compiler not found for llvm@11.0.0+clang+lld+lldb]
```

Changing the regex to only match until the end of the line fixes these
problems.

Fixes: #19473

0 files changed, 0 insertions, 0 deletions