Implement ~line_maps ()

Implement ~line_maps ()

line_maps instances such as the global line_table are
GC-managed, but the htab within location_adhoc_data_map.htab
is not GC-managed.

Previously this was deleted manually by a call to
location_adhoc_data_fini within toplev::main.

However, on adding a call to forcibly_ggc_collect after the
selftests, all of the htabs for the various line_tables
created during the selftests start showing up as leaks
in "make selftest-valgrind", e.g.:

13,536 (1,344 direct, 12,192 indirect) bytes in 12 blocks are definitely lost in loss record 1,065 of 1,086
   at 0x4A081D4: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x16DB3B0: xcalloc (xmalloc.c:163)
   by 0x16D8D34: htab_create_typed_alloc (hashtab.c:358)
   by 0x16D8DBD: htab_create_alloc (hashtab.c:286)
   by 0x16A2CCC: linemap_init(line_maps*, unsigned int) (line-map.c:353)
   by 0x1685605: selftest::line_table_test::line_table_test(selftest::line_table_case const&) (input.c:1624)
   by 0x167D09C: selftest::test_applying_fixits_modernize_named_init(selftest::line_table_case const&) (edit-context.c:1430)
   by 0x1686827: selftest::for_each_line_table_case(void (*)(selftest::line_table_case const&)) (input.c:3227)
   by 0x167F067: selftest::edit_context_c_tests() (edit-context.c:1658)
   by 0x1616E67: selftest::run_tests() (selftest-run-tests.c:71)
   by 0xC0DB25: toplev::run_self_tests() (toplev.c:2076)
   by 0x618EB4: toplev::main(int, char**) (toplev.c:2153)

This patch removes the manual one-time cleanup in favor of
adding a destructor to class line_maps, which cleans up
the non-GC-managed htab.

Doing so improves "make selftest-valgrind" from:

==61118== LEAK SUMMARY:
==61118==    definitely lost: 121,248 bytes in 1,515 blocks
==61118==    indirectly lost: 974,344 bytes in 959 blocks
==61118==      possibly lost: 0 bytes in 0 blocks
==61118==    still reachable: 1,332,599 bytes in 3,684 blocks
==61118==         suppressed: 0 bytes in 0 blocks

to:

==57182== LEAK SUMMARY:
==57182==    definitely lost: 13,840 bytes in 556 blocks
==57182==    indirectly lost: 0 bytes in 0 blocks
==57182==      possibly lost: 0 bytes in 0 blocks
==57182==    still reachable: 1,355,703 bytes in 3,684 blocks
==57182==         suppressed: 0 bytes in 0 blocks

gcc/ChangeLog:
	* toplev.c (toplev::main): Remove call to
	location_adhoc_data_fini.

libcpp/ChangeLog:
	* include/line-map.h (line_maps::~line_maps): New dtor.
	(location_adhoc_data_fini): Delete decl.
	* line-map.c (line_maps::~line_maps): New dtor.
	(location_adhoc_data_fini): Delete.

From-SVN: r241533