lto/122515: Fix archive offset types for i686

lto/122515: Fix archive offset types for i686

On i686, offsets into object archives could be 64-bit, but they're
inconsistently treated across the lto, which may sometimes result in
truncation of those offsets for large archives.

Use int64_t/off_t consistently across all uses of archive offsets to
make sure that they're always read and mapped correctly.

gcc/lto/ChangeLog

	PR lto/122515
	* lto.h (lto_section_slot): Set type of START to off_t.
	* lto-common.cc (lto_read_section_data): Adjust.
	* lto-object.cc (lto_obj_file_open): Set type of OFFSET to
	int64_t.

gcc/ChangeLog

	PR lto/122515
	* lto-wrapper.cc (debug_objcopy): Set type of INOFF to int64_t.
	(run_gcc): Set type of FILE_OFFSET to int64_t.

gcc/testsuite/ChangeLog

	PR lto/122515
	* lib/lto.exp (lto-build-archive): New procedure.
	(lto-execute-1): Use it.
	(lto-link-and-maybe-run, lto-get-options-main): Handle ar-link.
	* gcc.dg/lto/pr122515_0.c: New test case.
	* gcc.dg/lto/pr122515_1.c: New file.
	* gcc.dg/lto/pr122515_2.c: Likewise.
	* gcc.dg/lto/pr122515_3.c: Likewise.
	* gcc.dg/lto/pr122515_4.c: Likewise.
	* gcc.dg/lto/pr122515_5.c: Likewise.
	* gcc.dg/lto/pr122515_6.c: Likewise.
	* gcc.dg/lto/pr122515_7.c: Likewise.
	* gcc.dg/lto/pr122515_8.c: Likewise.
	* gcc.dg/lto/pr122515_9.c: Likewise.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>