Add support to the Xtensa target for creating trampolines for out-of-range branches.

* tc-xtensa.c (xtensa_check_frag_count, xtensa_create_trampoline_frag)
    (xtensa_maybe_create_trampoline_frag, init_trampoline_frag)
    (find_trampoline_seg, search_trampolines, get_best_trampoline)
    (check_and_update_trampolines, add_jump_to_trampoline)
    (dump_trampolines): New function.
    (md_parse_option): Add cases for --[no-]trampolines options.
    (md_assemble, finish_vinsn, xtensa_end): Add call to
    xtensa_check_frag_count.
    (xg_assemble_vliw_tokens): Add call to
    xtensa_maybe_create_trampoline_frag.
    (xtensa_relax_frag): Relax fragments with RELAX_TRAMPOLINE state.
    (relax_frag_immed): Relax jump instructions that cannot reach its
    target.
    * tc-xtensa.h (xtensa_relax_statesE::RELAX_TRAMPOLINE): New relax
    state.

    * as.texinfo: Document --[no-]trampolines command-line options.
    * c-xtensa.texi: Document trampolines relaxation and command line
    options.

    * frags.c (get_frag_count, clear_frag_count): New function.
    (frag_alloc): Increment totalfrags counter.
    * frags.h (get_frag_count, clear_frag_count): New function.

    * all.exp: Add test for trampoline relaxation.
    * trampoline.d: Trampoline relaxation expected dump.
    * trampoline.s: Trampoline relaxation test source.

gas/frags.c

@@ -24,6 +24,20 @@
 
 extern fragS zero_address_frag;
 extern fragS predefined_address_frag;
+
+static int totalfrags;
+
+int
+get_frag_count (void)
+{
+  return totalfrags;
+}
+
+void
+clear_frag_count (void)
+{
+  totalfrags = 0;
+}
 
 /* Initialization for frag routines.  */
 
@@ -70,6 +84,7 @@ frag_alloc (struct obstack *ob)
   ptr = (fragS *) obstack_alloc (ob, SIZEOF_STRUCT_FRAG);
   obstack_alignment_mask (ob) = oalign;
   memset (ptr, 0, SIZEOF_STRUCT_FRAG);
+  totalfrags++;
   return ptr;
 }