procedure-properties for RTL functions

procedure-properties for RTL functions

* module/system/vm/assembler.scm (link-procprops, link-objects): Arrange
  to write procedure property links out to a separate section.

* libguile/procprop.c (scm_procedure_properties):
* libguile/programs.h:
* libguile/programs.c (scm_i_rtl_program_properties):
* module/system/vm/debug.scm (find-program-properties): Wire up
  procedure-properties for RTL procedures.  Yeah!  Fistpumps!  :)

* module/system/vm/debug.scm (find-program-debug-info): Return #f if the
  string is "", as it is if we don't have a name.  Perhaps
  elf-symbol-name should return #f in that case...

* test-suite/tests/rtl.test: Add some tests.