rustavailable error is not helpful when clang isn't installed

[wedsonaf]

I ran make LLVM=1 rustavailable on a new system and got a hepful (as expected) message complaining about by my rustc version, but after fixing that, it failed as follows:

$ make LLVM=1 rustavailable
./scripts/rust_is_available.sh: 21: arithmetic expression: expecting primary: "100000 *  + 100 *  + "

The problem turned out to be that I didn't have a clang installed. After installing it, the message became helpful again (having to do with missing source code for core).

[ojeda]

https://lore.kernel.org/rust-for-linux/20230109204520.539080-3-ojeda@kernel.org/ should fix that (the patch series will have a v2)

[ojeda]

This is #934, so closing too.

[ojeda]

For reference, without Clang installed, this now gives:

***
*** Running 'bindgen' to check the libclang version (used by the Rust
*** bindings generator) failed with code 101. This may be caused by
*** a failure to locate libclang. See output and docs below for details:
***
thread 'main' panicked at 'Unable to find libclang: "couldn't find any valid shared libraries matching: ['libclang.so', 'libclang-*.so', 'libclang.so.*', 'libclang-*.so.*'], set the `LIBCLANG_PATH` environment variable to a path where one of these files can be found (invalid: [])"', /root/.cargo/registry/src/github.com-1ecc6299db9ec823/bindgen-0.56.0/src/lib.rs:1922:31
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
***
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***