gdb/jit: enable tracking multiple JITer objfiles

gdb/jit: enable tracking multiple JITer objfiles

GDB's JIT handler stores an objfile (and data associated with it) per
program space to keep track of JIT breakpoint information.  This assumes
that there is at most one JITer objfile in the program space.  However,
there may be multiple.  If so, only the first JITer's hook breakpoints
would be realized and the JIT events from the other JITers would be
missed.

This patch removes that assumption, allowing an arbitrary number of
objfiles within a program space to be JITers.

- The "unique" program_space -> JITer objfile pointer in
  jit_program_space_data is removed.  In fact, jit_program_space_data
  becomes empty, so it is removed entirely.

- jit_breakpoint_deleted is modified, it now has to assume that any
  objfile in a program space is a potential JITer.  It now iterates on
  all objfiles, checking if they are indeed JITers, and if they are,
  whether the deleted breakpoint belongs to them.

- jit_breakpoint_re_set_internal also has to assume that any objfile in
  a program space is a potential JITer.  It creates (or updates) one
  jiter_objfile_data structure for each JITer it finds.

- Same for jit_inferior_init.  It now iterates all objfiles to read the
  initial JIT object list.

gdb/ChangeLog:
2020-07-22  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>
	    Simon Marchi  <simon.marchi@polymtl.ca>

	* jit.c (struct jit_program_space_data): Remove.
	(jit_program_space_key): Remove.
	(jiter_objfile_data::~jiter_objfile_data): Remove program space
	stuff.
	(get_jit_program_space_data): Remove.
	(jit_breakpoint_deleted): Iterate on all of the program space's
	objfiles.
	(jit_inferior_init): Likewise.
	(jit_breakpoint_re_set_internal): Likewise.  Also change return
	type to void.
	(jit_breakpoint_re_set): Pass current_program_space to
	jit_breakpoint_re_set_internal.

gdb/testsuite/ChangeLog:
2020-07-22  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* gdb.base/jit-reader-simple.exp: Add a scenario for a binary that
	loads two JITers.