PR46, cygwin: FAIL: cdtest with -Ur

See the comment in pe.sc to understand why ld -Ur won't work.

	PR 46
binutils/
	* testsuite/lib/binutils-common.exp (is_pecoff_format): Rewrite
	with positive logic and add more target triples.
ld/
	* scripttempl/pe.sc: Comment on ld -Ur fail.  Wrap .gcc_exc comment.
	* scripttempl/pep.sc: Likewise.
	* testsuite/ld-cdtest/cdtest.exp (test2): xfail for pe.

binutils/testsuite/lib/binutils-common.exp

@@ -95,14 +95,17 @@ proc is_aout_format {} {
 # True if the object format is known to be PE COFF.
 #
 proc is_pecoff_format {} {
-    if { ![istarget *-*-mingw*]
-	 && ![istarget *-*-cygwin*]
-	 && ![istarget *-*-cegcc*]
-	 && ![istarget *-*-pe*] } {
-	return 0
+    if { [istarget *-*-beospe*]
+	 || [istarget *-*-cegcc*]
+	 || [istarget *-*-cygwin*]
+	 || [istarget *-*-interix*]
+	 || [istarget *-*-mingw*]
+	 || [istarget *-*-netbsdpe*]
+	 || [istarget *-*-pe*]
+	 || [istarget *-*-winnt*] } {
+	return 1
     }
-
-    return 1
+    return 0
 }
 
 proc is_som_format {} {