runtest.exp: add libdirs list for load_lib()

libgomp wants to load .exp files from ../gcc/testsuite/lib.
Instrument load_lib to be able to find the files.
Previously we used to have a helper proc that had to first load all
dependent .exp manually and then, again manually, the desired .exp.

2012-03-16  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>

	* runtest.exp (libdirs): New global list.
	(load_lib): Append libdirs to search_and_load_files directories.

diff --git a/runtest.exp b/runtest.exp
index 4bfed83..8e6a7de 100644
--- a/runtest.exp
+++ b/runtest.exp
@@ -589,7 +589,7 @@ proc lookfor_file { dir name } {
 # source tree, (up one or two levels), then in the current dir.
 #
 proc load_lib { file } {
-    global verbose libdir srcdir base_dir execpath tool
+    global verbose libdir libdirs srcdir base_dir execpath tool
     global loaded_libs
 
     if {[info exists loaded_libs($file)]} {
@@ -597,8 +597,11 @@ proc load_lib { file } {
     }
 
     set loaded_libs($file) ""
-
-    if { [search_and_load_file "library file" $file [list ../lib $libdir $libdir/lib [file dirname [file dirname $srcdir]]/dejagnu/lib $srcdir/lib $execpath/lib . [file dirname [file dirname [file dirname $srcdir]]]/dejagnu/lib]] == 0 } {
+    set search_dirs [list ../lib $libdir $libdir/lib [file dirname [file dirname $srcdir]]/dejagnu/lib $srcdir/lib $execpath/lib . [file dirname [file dirname [file dirname $srcdir]]]/dejagnu/lib]
+    if {[info exists libdirs]} {
+        lappend search_dirs $libdirs
+    }
+    if { [search_and_load_file "library file" $file $search_dirs ] == 0 } {
 	send_error "ERROR: Couldn't find library file $file.\n"
 	exit 1
     }
@@ -652,6 +655,8 @@ set libdir   [file dirname $execpath]/dejagnu
 if {[info exists env(DEJAGNULIBS)]} {
     set libdir $env(DEJAGNULIBS)
 }
+# list of extra directories for load_lib
+set libdirs {}
 
 verbose "Using $libdir to find libraries"