7008325: CodeCache exhausted on sparc starting from hs20b04

Remove clear_scratch_buffer_blob and let init_scratch_buffer_blob free and allocate a new blob if required.

Reviewed-by: twisti

hotspot/src/share/vm/memory/heap.hpp

@@ -161,6 +161,7 @@ class CodeHeap : public CHeapObj {
   size_t max_capacity() const;
   size_t allocated_capacity() const;
   size_t unallocated_capacity() const            { return max_capacity() - allocated_capacity(); }
+  size_t largest_free_block() const;
 
   // Debugging
   void verify();