ELF: Scan for dylibs-as-objects when adding rpaths

Shared libraries can be provided on the command line as if they were
objects, as a path to the ".so" file. The "each-lib-rpath" functionality
was ignoring these shared libraries accidentally, causing missing rpaths
in the output executable.

Author: topolarity

src/link/Elf.zig

@@ -1592,6 +1592,21 @@ fn linkWithLLD(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node) !v
                     }
                 }
             }
+            for (self.base.options.objects) |obj| {
+                // Libraries may appear as object files on the command line, so we scan
+                // for them here (looking for ".so", ".so.X", ".so.X.Y", etc.)
+                var it = std.mem.split(u8, std.fs.path.basename(obj.path), ".");
+                _ = it.next();
+                const suffix = it.next() orelse continue;
+
+                if (std.mem.startsWith(u8, suffix, target.dynamicLibSuffix()[1..])) {
+                    const lib_dir_path = std.fs.path.dirname(obj.path).?;
+                    if ((try rpath_table.fetchPut(lib_dir_path, {})) == null) {
+                        try argv.append("-rpath");
+                        try argv.append(lib_dir_path);
+                    }
+                }
+            }
         }
 
         for (self.base.options.lib_dirs) |lib_dir| {