Fix addend handling and other cleanups for s390

[jpoimboe]

Several improvements for issues discovered in the review for #1203 .Mostly related to addend handling, but also some other cleanups and an endianness fix.

[joe-lawrence]

Hi @jpoimboe ,

Check out the internal automated integration test failure emails, there are various complaints like these:

create-diff-object: ERROR: af_netlink.o: kpatch_replace_sections_syms: 1609: .text.jhash+0x95: 
can't find replacement symbol for .rodata.jhash+0 reference

create-diff-object: ERROR: sys.o: kpatch_replace_sections_syms: 1609: .text.prctl_set_mm+0x1c7:
can't find replacement symbol for .rodata.prctl_set_mm+0 reference

create-diff-object: ERROR: fib_frontend.o: kpatch_replace_sections_syms: 1609: .text.rtm_to_fib_config+0x13a:
can't find replacement symbol for .rodata.rtm_to_fib_config+0 reference

create-diff-object: ERROR: array.o: kpatch_replace_sections_syms: 1609: .text.proc_pid_status+0x619:
can't find replacement symbol for .rodata.proc_pid_status+0 reference

[jpoimboe]

Going to squash in this change to fix the integration failures:

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index 8345b16..bebe3bd 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -1604,7 +1604,7 @@ static void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
                        }
 
                        if (!found && !is_string_literal_section(rela->sym->sec) &&
-                           strcmp(rela->sym->name, ".rodata")) {
+                           strncmp(rela->sym->name, ".rodata", 7)) {
                                ERROR("%s+0x%x: can't find replacement symbol for %s+%ld reference",
                                      relasec->base->name, rela->offset, rela->sym->name, rela->addend);
                        }

[jpoimboe]

v2:

• refine .rodata check in missing replacement symbol warning