[libgpiod][bug] building rust bindings requires clang headers

[Kent Gibson <warthog618@xxxxxxxxx>]

When trying to build the libgpiod rust bindings on my Debian bullseye VM I get:

   Compiling gpiosim-sys v0.1.0 (/home/dev/libgpiod/bindings/rust/gpiosim-sys)
error: failed to run custom build command for `gpiosim-sys v0.1.0 (/home/dev/libgpiod/bindings/rust/gpiosim-sys)`

Caused by:
  process didn't exit successfully: `/home/dev/libgpiod/bindings/rust/target/release/build/gpiosim-sys-dfa257ecee3f0e2e/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=../../../tests/gpiosim/gpiosim.h

  --- stderr
  ../../../tests/gpiosim/gpiosim.h:7:10: fatal error: 'stdbool.h' file not found
  thread 'main' panicked at 'Unable to generate bindings: ClangDiagnostic("../../../tests/gpiosim/gpiosim.h:7:10: fatal error: 'stdbool.h' file not found\n")', gpiosim-sys/build.rs:27:10
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The source of the error appears to be bindgen using libclang to parse
the gpiosim header, and that failing if the requisite headers are not
installed.

If I install them:

apt install libclang-common-11-dev

the build passes.

Can a dependency be added to the autotools configuration to check for
the availability of those headers if building the rust bindings?
I would add it myself, but I'm not sure how - or if there is some better
solution.
The configure.ac already has a AC_HEADER_STDBOOL, but that checks for
the gcc headers, not clang.

Cheers,
Kent.