Fix ld tests with sysroot=/ and --enable-targets=all and test --print-sysroot

* ld-scripts/sysroot-prefix.exp: Log $ld_sysroot.  Handle sysroot
	== "/" as a separate sysroot-configuration with separable
	test-types.
	(sysroot_prefix_tests): Include all existing sysroot tests in
	sysroot == "/" tests except exclude those where a --sysroot option
	is not specified.
	* lib/ld-lib.exp (check_sysroot_available): Rewrite to use
	--print-sysroot instead of relying on error code from using
	--sysroot=...  Also, set $ld_sysroot.

The reason we exclude not just the failing "full-path =-prefixed
without" but also the passing "plain =-prefixed without but -Lpath"
for sysroot == "/" is that for the latter to succeed, we have to make
assumptions about the system not having a /sysroot directory or
assumptions about its contents etc.

When passing --enable-targets=all --enable-64-bit-bfd (the
latter not required for a "64-bit-host" of course) the ld --help
output got too much to handle for poor tcl (or maybe dejagnu is
to blame) and remote_exec exited with an error, so the
configuration being tested was mishandled as being a
sysroot-less configuration.  Using --version instead of --help
would work too, but the new --print-sysroot option calls for
nominal coverage, so why not use that instead.

ld/testsuite/ChangeLog

@@ -1,3 +1,15 @@
+2014-10-17  Hans-Peter Nilsson  <hp@axis.com>
+
+	* ld-scripts/sysroot-prefix.exp: Log $ld_sysroot.  Handle sysroot
+	== "/" as a separate sysroot-configuration with separable
+	test-types.
+	(sysroot_prefix_tests): Include all existing sysroot tests in
+	sysroot == "/" tests except exclude those where a --sysroot option
+	is not specified.
+	* lib/ld-lib.exp (check_sysroot_available): Rewrite to use
+	--print-sysroot instead of relying on error code from using
+	--sysroot=...  Also, set $ld_sysroot.
+
 2014-10-15  Hans-Peter Nilsson  <hp@axis.com>
 
 	* ld-scripts/sysroot-prefix.exp, ld-scripts/sysroot-prefix-x.s,

ld/testsuite/ld-scripts/sysroot-prefix.exp

@@ -27,14 +27,21 @@
 # present or not, with different arguments.
 
 # Find out if the linker supports sysroot; if it was configured
-# "--with-sysroot X".  We ignore that X can actually be set to
-# interfere with the tests, as that's unlikely to be useful, and
-# assume that the build-directory (aka. $base_dir) does not contain X.
+# "--with-sysroot X" where X is a non-empty string.
 set with_sysroot [check_sysroot_available]
-verbose -log "Has (non-empty) sysroot support: $with_sysroot"
+verbose -log "Has (non-empty) sysroot support: $with_sysroot; \"$ld_sysroot\""
+
+# We also need to know if the sysroot is "/" (a common use) as some of
+# the tests prepend sysroot to the current directory and on most
+# common systems "//dir/path" is handled as "/dir/path".
+if {$ld_sysroot == "/"} {
+    # Use a modified test-subset for testing.
+    set with_sysroot 3
+}
 
 # Entries in the array-tables:
-# 0: Testtype (1: only non-sysroot, 2: only sysroot, 3: either).
+# 0: Testtype; an inclusive bitmask indicating that the test should run on a
+# build configured for: 1: non-sysroot, 2: sysroot != "/", 4: sysroot == "/".
 # 1: Description, forming part of the dejagnu test-name.
 # 2: Replacement for @p@.
 # 3: Option to pass to linker (usually something with --sysroot).
@@ -47,16 +54,16 @@ verbose -log "Has (non-empty) sysroot support: $with_sysroot"
 # description contains @cwd@, that will be replaced by "<CWD>".
 
 set sysroot_prefix_tests {
-    {3 "plain -Lpath" "sysroot/" {} ""}
-    {3 "root-anchored but -Lpath" "/sysroot/" {} "cannot find"}
-    {3 "full-path" "@cwd@/sysroot/" {} ""}
-    {3 "root-anchored =-prefixed -Lpath" "=/sysroot/" {} "cannot find"}
-    {3 "full-path =-prefixed with empty" "=@cwd@/sysroot/" "--sysroot=" ""}
-    {3 "plain =-prefixed with empty" "=sysroot/" "--sysroot=" ""}
-    {2 "root-anchored but script outside sysroot" "/" "--sysroot=@cwd@/sysroot" "cannot find"}
-    {2 "root-anchored and script inside sysroot" "/sysroot/" "--sysroot=@cwd@" ""}
-    {2 "root-anchored =-prefixed script outside" "=/" "--sysroot=@cwd@/sysroot" ""}
-    {2 "root-anchored =-prefixed script inside" "=/sysroot/" "--sysroot=@cwd@" ""}
+    {7 "plain -Lpath" "sysroot/" {} ""}
+    {7 "root-anchored but -Lpath" "/sysroot/" {} "cannot find"}
+    {7 "full-path" "@cwd@/sysroot/" {} ""}
+    {7 "root-anchored =-prefixed -Lpath" "=/sysroot/" {} "cannot find"}
+    {7 "full-path =-prefixed with empty" "=@cwd@/sysroot/" "--sysroot=" ""}
+    {7 "plain =-prefixed with empty" "=sysroot/" "--sysroot=" ""}
+    {6 "root-anchored but script outside sysroot" "/" "--sysroot=@cwd@/sysroot" "cannot find"}
+    {6 "root-anchored and script inside sysroot" "/sysroot/" "--sysroot=@cwd@" ""}
+    {6 "root-anchored =-prefixed script outside" "=/" "--sysroot=@cwd@/sysroot" ""}
+    {6 "root-anchored =-prefixed script inside" "=/sysroot/" "--sysroot=@cwd@" ""}
     {2 "plain =-prefixed without but -Lpath" "=sysroot/" {} "cannot find"}
     {2 "full-path =-prefixed without" "=@cwd@/sysroot/" {} "cannot find"}
     {1 "plain =-prefixed -Lpath" "=sysroot/" {} ""}

ld/testsuite/lib/ld-lib.exp

@@ -1669,16 +1669,14 @@ proc check_plugin_api_available { } {
     return $plugin_api_available_saved
 }
 
-# Returns true if the target ld supports sysroot.
+# Sets ld_sysroot to the current sysroot (empty if not supported) and
+# returns true if the target ld supports sysroot.
 proc check_sysroot_available { } {
-    global ld_sysroot_available_saved
-    global ld
+    global ld_sysroot_available_saved ld ld_sysroot
     if {![info exists ld_sysroot_available_saved]} {
-	# Check if ld supports --sysroot *other* than empty
-	# (non-sysroot linkers don't emit errors for --sysroot="").
-	# The help-text by itself is no indication as it always lists --sysroot.
-	set status [remote_exec host $ld "--sysroot=ldxyzzy --help >/dev/null"]
-	if { [lindex $status 0] != 0 } {
+	# Check if ld supports --sysroot *other* than empty.
+	set ld_sysroot [string trimright [lindex [remote_exec host $ld "--print-sysroot"] 1]]
+	if { $ld_sysroot == "" } {
 	    set ld_sysroot_available_saved 0
 	} else {
 	    set ld_sysroot_available_saved 1