allow auto_bitmap to use other bitmap obstacks

gcc/ChangeLog:

2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* bitmap.h (class auto_bitmap): New constructor taking
	bitmap_obstack * argument.

From-SVN: r248018

gcc/ChangeLog

 2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
 
+	* bitmap.h (class auto_bitmap): New constructor taking
+	bitmap_obstack * argument.
+
+2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
+
 	* bitmap.h (class auto_bitmap): Change type of m_bits to
 	bitmap_head, and adjust ctor / dtor and member operators.
 

gcc/bitmap.h

@@ -807,6 +807,7 @@ class auto_bitmap
 {
  public:
   auto_bitmap () { bitmap_initialize (&m_bits, &bitmap_default_obstack); }
+  explicit auto_bitmap (bitmap_obstack *o) { bitmap_initialize (&m_bits, o); }
   ~auto_bitmap () { bitmap_clear (&m_bits); }
   // Allow calling bitmap functions on our bitmap.
   operator bitmap () { return &m_bits; }