configure.ac: LIBPATHENV on macOS

* configure.ac (LIBPATHENV): use DYLD_FALLBACK_LIBRARY_PATH instead of
  DYLD_LIBRARY_PATH on macOS, to honor runtime paths embedded in the
  binaries.  [ruby-core:88487] [Bug #14992]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64392 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.ac

@@ -2588,7 +2588,7 @@ AS_IF([test "$with_dln_a_out" != yes], [
 			rb_cv_dlopen=yes],
 	[darwin*], [	: ${LDSHARED='$(CC) -dynamic -bundle'}
 			: ${LDFLAGS=""}
-			: ${LIBPATHENV=DYLD_LIBRARY_PATH}
+			: ${LIBPATHENV=DYLD_FALLBACK_LIBRARY_PATH}
 			: ${PRELOADENV=DYLD_INSERT_LIBRARIES}
 			rb_cv_dlopen=yes],
         [aix*], [	: ${LDSHARED='$(CC)'}