$ git clone https://github.com/rust-onig/rust-onig.git
$ cd rust-onig
$ git log -n 1
commit 1de4269744c23c8f59d3335077213f85e0a29e18
Author: Will Speak <lithiumflame@gmail.com>
Date:   Tue Oct 1 07:11:03 2019 +0100

    Update `pkg-config` Crate to Fix Missing CFLAGS

    Some platforms require `pkgconfig` to be told to include system CFLAGS
    otherwise we can't compile against the system copy of `onig`. This
    updates the dependent crate to fix the issue.

    Fixes: #119
$ cargo clean
$ cargo build
...
   Compiling onig_sys v69.2.0 (/home/qtfkwk/rust-onig/rust-onig/onig_sys)
error: failed to run custom build command for `onig_sys v69.2.0 (/home/qtfkwk/rust-onig/rust-onig/onig_sys)`

Caused by:
  process didn't exit successfully: `/home/qtfkwk/rust-onig/rust-onig/target/debug/build/onig_sys-0975fb7a2420ab75/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'Unable to find libclang: "the `libclang` shared library at /usr/lib64/clang-private/libclang.so.7 could not be opened: libclangAST.so.7: cannot open shared object file: No such file or directory"', src/libcore/result.rs:1084:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

$ rustup update
...
   stable-x86_64-unknown-linux-gnu unchanged - rustc 1.38.0 (625451e37 2019-09-23)
  nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.40.0-nightly (032a53a06 2019-10-03)

$ ls -lh libclang{,AST}.*
lrwxrwxrwx. 1 root root   16 Oct  1 14:46 libclangAST.so -> libclangAST.so.7
-rwxr-xr-x. 1 root root 3.5M Jan 24  2019 libclangAST.so.7
lrwxrwxrwx. 1 root root   13 Oct  1 14:46 libclang.so -> libclang.so.7
-rwxr-xr-x. 1 root root 546K Jan 24  2019 libclang.so.7

$ file /usr/lib64/clang-private/libclang{,AST}.so.7
/usr/lib64/clang-private/libclang.so.7:    ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, BuildID[sha1]=8585019abeba38846686d1a1a2a1852a0102466f, stripped
/usr/lib64/clang-private/libclangAST.so.7: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, BuildID[sha1]=af53e177be1768c1becd8b39d871b24beacfc676, stripped

$ sudo yum check-updates >/dev/null; echo $?
0