gdb/sim: add support for exporting memory map

This allows gdb to quickly dump & process the memory map that the sim
knows about.  This isn't fully accurate, but is largely limited by the
gdb memory map format.  While the sim supports RWX bits, gdb can only
handle RW or RO regions.

include/gdb/ChangeLog

@@ -1,3 +1,7 @@
+2021-01-07  Mike Frysinger  <vapier@gentoo.org>
+
+	* remote-sim.h (sim_memory_map): Define.
+
 2016-07-15  John Baldwin  <jhb@FreeBSD.org>
 
 	* signals.def: Add GDB_SIGNAL_LIBRT.

include/gdb/remote-sim.h

@@ -213,6 +213,15 @@ int sim_store_register (SIM_DESC sd, int regno, unsigned char *buf, int length);
 void sim_info (SIM_DESC sd, int verbose);
 
 
+/* Return a memory map in XML format.
+
+   The caller must free the returned string.
+
+   For details on the format, see GDB's Memory Map Format documentation.  */
+
+char *sim_memory_map (SIM_DESC sd);
+
+
 /* Run (or resume) the simulated program.
 
    STEP, when non-zero indicates that only a single simulator cycle