Partially revert JuliaLang#42919 (JuliaLang#42969)

* Partially revert JuliaLang#42919

The change to RPATH setting for macOS seems to have improved the
situation for users on Monterey, but the other changes in JuliaLang#42919 that
affect other platforms seem to have caused regressions on musl Linux
(JuliaLang#42940) and FreeBSD (JuliaLang#42944). The easiest thing to do here is to keep
the changes from JuliaLang#42919 as they apply to macOS but revert the others.

* Un-revert the `RPATH_LIB` definition

Make.inc

@@ -1198,7 +1198,7 @@ else ifeq ($(OS), Darwin)
  RPATH_ESCAPED_ORIGIN := $(RPATH_ORIGIN)
  RPATH_LIB := -Wl,-rpath,'@loader_path/'
 else
- RPATH := -Wl,-rpath,'$$ORIGIN/$(build_libdir_rel)' -Wl,-rpath-link,$(build_shlibdir) -Wl,-z,origin
+ RPATH := -Wl,-rpath,'$$ORIGIN/$(build_libdir_rel)' -Wl,-rpath,'$$ORIGIN/$(build_private_libdir_rel)' -Wl,-rpath-link,$(build_shlibdir) -Wl,-z,origin
  RPATH_ORIGIN := -Wl,-rpath,'$$ORIGIN' -Wl,-z,origin
  RPATH_ESCAPED_ORIGIN := -Wl,-rpath,'\$$\$$ORIGIN' -Wl,-z,origin -Wl,-rpath-link,$(build_shlibdir)
  RPATH_LIB := -Wl,-rpath,'$$ORIGIN/' -Wl,-z,origin