[llvm] [llvm-objdump] Add --substitute-path and --source-dir for --source (PR #201096)

[James Henderson via llvm-commits]

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@@ -4,13 +4,13 @@
 ;; lives in this test's Inputs directory. Without path remapping, --source
 ;; cannot load the file from disk.
 ;;
-;; --source-dir: each flag is prepended to the search list, so later flags on
-;; the command line are tried first.
+;; --source-dir: one directory per flag; later flags on the command line are
+;; searched before earlier ones.
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jh7370 wrote:

I think this behaviour is backwards. Consider either how the `PATH` environment variable or perhaps more significantly include paths (-I in the compiler) are searched: they are always first to last. Of course, "default" paths (i.e. those not specified via the option) should be searched after those specified by the option.

https://github.com/llvm/llvm-project/pull/201096