Fix another typo

From-SVN: r99750

gcc/testsuite/lib/compat.exp

@@ -289,6 +289,7 @@ proc compat-execute { src1 sid use_alt } {
     }
     if {[string first "$tmpdir/" "$testcase"] == 0} {
 	set testcase [string range "$testcase" [string length "$tmpdir/"] end]
+	set testcase "tmpdir-$testcase"
     }
     regsub "_main.*" $testcase "" testcase
     # Set up the base name of executable files so they'll be unique.