Fix test to not depend on DECL_UIDs

 Fix test to not depend on DECL_UIDs

The tester started tripping this on s390-linux-gnu:

Tests that now fail, but worked before (19 tests):

gcc.dg/pr96542.c scan-tree-dump-times evrp "254" 2

The problem is we search for "254" in the dump file.  The dump file contains
UIDs for function declarations.  So changes in the number of predefined DECL
nodes can make the test pass or file depending on whether or not a decl with
a UID containing "254" shows up.  Like this:

;; Function foo (foo, funcdef_no=0, decl_uid=2542, cgraph_uid=1, symbol_order=0)

ISTM the test wants to look for a "return 254" rather than just "254".
I added a change for that to the tester.  Naturally that fixed the test on
s390 and the dozen or so targets I tested didn't show any regressions.

gcc/testsuite
	* gcc.dg/pr96542.c: Avoid falsely matching DECL_UIDs with
	the number 254 in them.