Fix double-free when creating more than one block in JIT debug info reader

Fix double-free when creating more than one block in JIT debug info reader

A double-free happens when using a JIT debug info reader that creates
more than one block.  In the loop that frees blocks in finalize_symtab,
at the very end, the gdb_block_iter_tmp variable is set initially, but
not changed as the loop advances.  If we have two blocks, the first
iteration frees the first block, the second iteration frees the second
block, but the third iteration tries to free the second block again, as
gdb_block_iter_tmp keeps pointing on the second block.

Fix it by assigning the gdb_block_iter_tmp variable in the loop.

I have improved the jit-reader.exp test to cover this case, by adding a
second "JIT-ed" function and creating a block for it.  I have renamed
the existing function to something I find a bit more descriptive.  There
are no significant changes to jit-reader.exp itself, only updates
following the renaming.  The important changes are in jithost.c
(generate a new function) and in jitreader.c (create a gdb_block for
that function).

This was found because of an ASan report:

$ ./gdb testsuite/outputs/gdb.base/jit-reader/jit-reader -ex "jit-reader-load /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/jit-reader/jitreader.so" -ex r
Reading symbols from testsuite/outputs/gdb.base/jit-reader/jit-reader...
Starting program: /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/jit-reader/jit-reader
=================================================================
==1751048==ERROR: AddressSanitizer: heap-use-after-free on address 0x604000042eb8 at pc 0x5650ef8eec88 bp 0x7ffe52767290 sp 0x7ffe52767280
READ of size 8 at 0x604000042eb8 thread T0
    #0 0x5650ef8eec87 in finalize_symtab /home/simark/src/binutils-gdb/gdb/jit.c:768
    #1 0x5650ef8eef88 in jit_object_close_impl /home/simark/src/binutils-gdb/gdb/jit.c:797
    #2 0x7fbbda986278 in read_debug_info /home/simark/src/binutils-gdb/gdb/testsuite/gdb.base/jitreader.c:71
    #3 0x5650ef8ef56b in jit_reader_try_read_symtab /home/simark/src/binutils-gdb/gdb/jit.c:850
    #4 0x5650ef8effe3 in jit_register_code /home/simark/src/binutils-gdb/gdb/jit.c:948
    #5 0x5650ef8f2c92 in jit_event_handler(gdbarch*) /home/simark/src/binutils-gdb/gdb/jit.c:1396
    #6 0x5650ef0d137e in handle_jit_event /home/simark/src/binutils-gdb/gdb/breakpoint.c:5470
    [snip]

0x604000042eb8 is located 40 bytes inside of 48-byte region [0x604000042e90,0x604000042ec0)
freed by thread T0 here:
    #0 0x7fbbe57376b0 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:122
    #1 0x5650ef8f350b in xfree<gdb_block> /home/simark/src/binutils-gdb/gdb/gdbsupport/common-utils.h:62
    #2 0x5650ef8eeca9 in finalize_symtab /home/simark/src/binutils-gdb/gdb/jit.c:769
    #3 0x5650ef8eef88 in jit_object_close_impl /home/simark/src/binutils-gdb/gdb/jit.c:797
    #4 0x7fbbda986278 in read_debug_info /home/simark/src/binutils-gdb/gdb/testsuite/gdb.base/jitreader.c:71
    #5 0x5650ef8ef56b in jit_reader_try_read_symtab /home/simark/src/binutils-gdb/gdb/jit.c:850
    #6 0x5650ef8effe3 in jit_register_code /home/simark/src/binutils-gdb/gdb/jit.c:948
    #7 0x5650ef8f2c92 in jit_event_handler(gdbarch*) /home/simark/src/binutils-gdb/gdb/jit.c:1396
    #8 0x5650ef0d137e in handle_jit_event /home/simark/src/binutils-gdb/gdb/breakpoint.c:5470
    [snip]

previously allocated by thread T0 here:
    #0 0x7fbbe5737cd8 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:153
    #1 0x5650eef662f3 in xcalloc /home/simark/src/binutils-gdb/gdb/alloc.c:100
    #2 0x5650ef8f34ea in xcnew<gdb_block> /home/simark/src/binutils-gdb/gdb/gdbsupport/poison.h:122
    #3 0x5650ef8ed467 in jit_block_open_impl /home/simark/src/binutils-gdb/gdb/jit.c:557
    #4 0x7fbbda98620a in read_debug_info /home/simark/src/binutils-gdb/gdb/testsuite/gdb.base/jitreader.c:60
    #5 0x5650ef8ef56b in jit_reader_try_read_symtab /home/simark/src/binutils-gdb/gdb/jit.c:850
    #6 0x5650ef8effe3 in jit_register_code /home/simark/src/binutils-gdb/gdb/jit.c:948
    #7 0x5650ef8f2c92 in jit_event_handler(gdbarch*) /home/simark/src/binutils-gdb/gdb/jit.c:1396
    #8 0x5650ef0d137e in handle_jit_event /home/simark/src/binutils-gdb/gdb/breakpoint.c:5470
    [snip]

gdb/ChangeLog:

	* jit.c (finalize_symtab): Set gdb_block_iter_tmp in loop.

gdb/testsuite/ChangeLog:

	* gdb.base/jit-reader.exp (jit_reader_test): Rename
	jit_function_00 to jit_function_stack_mangle.
	* gdb.base/jithost.c (jit_function_t): Rename to...
	(jit_function_stack_mangle_t): ... this.
	(jit_function_add_t): New typedef.
	(jit_function_00_code): Rename to...
	(jit_function_stack_mangle_code): ... this, make static.
	(jit_function_add_code): New.
	(main): Generate "add" function and call it.  Adjust to changes
	in jithost_abi.
	* gdb.base/jithost.h (struct jithost_abi_bounds): New.
	(struct jithost_abi) <begin, end>: Remove fields.
	<object, function_stack_mangle, function_add>: New fields.
	* gdb.base/jitreader.c (struct reader_state) <code_begin,
	code_end>: Remove fields.
	<func_stack_mangle>: New field.
	(read_debug_info): Adjust to renaming, create block for "add"
	function.
	(read_sp, unwind_frame, get_frame_id): Adjust to other changes.