ggc-common: Fix save PCH assertion

We are getting a gnuradio PCH ICE
/usr/include/pybind11/stl.h:447:1: internal compiler error: in gt_pch_save, at ggc-common.cc:693
0x1304e7d gt_pch_save(_IO_FILE*)
        ../../gcc/ggc-common.cc:693
0x12a45fb c_common_write_pch()
        ../../gcc/c-family/c-pch.cc:175
0x18ad711 c_parse_final_cleanups()
        ../../gcc/cp/decl2.cc:5062
0x213988b c_common_parse_file()
        ../../gcc/c-family/c-opts.cc:1319
(unfortunately it isn't reproduceable always, but often needs
up to 100 attempts, isn't reproduceable in a cross etc.).
The bug is in the assertion I've added in gt_pch_save when adding
relocation support for the PCH files in case they happen not to be
mmapped at the selected address.
addr is a relocated address which points to a location in the PCH
blob (starting at mmi.preferred_base, with mmi.size bytes) which contains
a pointer that needs to be relocated.  So the assertion is meant to
verify the address is within the PCH blob, obviously it needs to be
equal or above mmi.preferred_base, but I got the other comparison wrong
and when one is very unlucky and the last sizeof (void *) bytes of the
blob happen to be a pointer which needs to be relocated, such as on the
s390x host addr 0x8008a04ff8, mmi.preferred_base 0x8000000000 and
mmi.size 0x8a05000, addr + sizeof (void *) is equal to mmi.preferred_base +
mmi.size and that is still fine, both addresses are end of something.

2024-02-03  Jakub Jelinek  <jakub@redhat.com>

	* ggc-common.cc (gt_pch_save): Allow addr to be equal to
	mmi.preferred_base + mmi.size - sizeof (void *).