[testsuite] dg-require-effective-target: skip unneeded checks

[Janis Johnson]

This patch causes dg-require-effective-target to return early if the
test is already being skipped, saving some work.  There's already
similar code in dg-skip-if.

OK for trunk, and later for 4.6?

2011-06-21  Janis Johnson  <jani...@codesourcery.com>

        * lib/target-supports-dg.exp (dg-require-effective-target): Return
        early if the test is already being skipped.

Index: lib/target-supports-dg.exp
===================================================================
--- lib/target-supports-dg.exp  (revision 175269)
+++ lib/target-supports-dg.exp  (working copy)
@@ -172,6 +172,12 @@
     if { [llength $args] < 1 || [llength $args] > 2 } {
        error "syntax error, need a single effective-target keyword with 
optional selector"
     }
+
+    # Don't bother if we're already skipping the test.
+    upvar dg-do-what dg-do-what
+    if { [lindex ${dg-do-what} 1] == "N" } {
+      return
+    }
     
     # Evaluate selector if present.
     if { [llength $args] == 2 } {
@@ -182,7 +188,6 @@
     }
 
     if { ![is-effective-target [lindex $args 0]] } {
-       upvar dg-do-what dg-do-what
         set dg-do-what [list [lindex ${dg-do-what} 0] "N" "P"]
     }
 }