Apply light cleaning

pgrx-pg-sys/build/clang.rs

@@ -52,11 +52,16 @@ pub(crate) fn detect_include_paths_for(
         clang_sys::get_library().expect("libclang should have been loaded?").path().to_owned();
     eprintln!("found libclang at {}", libclang_path.display());
     // libclang will probably be in a dynamic library directory,
-    // which means it will probably be adjacent to its headers
+    // which means it will probably be adjacent to its headers, e.g.
+    // - "/usr/lib/libclang-${CLANG_MAJOR}.so.${CLANG_MAJOR}.${CLANG_MINOR}"
+    // - "/usr/lib/clang/${CLANG_MAJOR}/include"
     let clang_major_fmt = clang_major.to_string();
     let mut paths = vec![];
-    let mut libclang_ancestors = libclang_path.ancestors();
-    while let Some(ancestor) = libclang_ancestors.next() {
+    // by adjacent, that does not mean it is always immediately so, e.g.
+    // - "/usr/lib/x86_64-linux-gnu/libclang-${CLANG_MAJOR}.so.${CLANG_MAJOR}.${CLANG_MINOR}.${CLANG_SUBMINOR}"
+    // - "/usr/lib/clang/${CLANG_MAJOR}/include"
+    // so, crawl back up the ancestral tree
+    for ancestor in libclang_path.ancestors() {
         paths = WalkDir::new(ancestor)
             .min_depth(1)
             .max_depth(6)
@@ -92,6 +97,7 @@ pub(crate) fn detect_include_paths_for(
                 }
             })
             .collect::<Vec<_>>();
+
         if paths.len() > 0 {
             paths.sort();
             paths.dedup();