[ELF][ARM64] Fix IFUNC relocations in -static-pie executables

For a static position-independent executable, a libc's intitialization
routine reads the dynamic relocation table and apply them. It looks like
on ARM64, they simply apply relocations from the begining of the table
to end. Therefore, if an IFUNC relocation appears before RELATIVE relocs,
the IFUNC resolver would see an unrelocated value. So, we need to place
RELATIVE relocs before IFUNCs.

Fixes #382

elf/output-chunks.cc

@@ -373,9 +373,9 @@ void RelDynSection<E>::sort(Context<E> &ctx) {
 
   auto get_rank = [](u32 r_type) {
     switch (r_type) {
-    case E::R_IRELATIVE: return 0;
-    case E::R_RELATIVE: return 1;
-    default: return 2;
+    case E::R_RELATIVE: return 0;
+    case E::R_IRELATIVE: return 2;
+    default: return 1;
     }
   };
 

elf/passes.cc

@@ -1287,10 +1287,10 @@ void fix_synthetic_symbols(Context<E> &ctx) {
   // the second attempt with wrong function addresses, causing a
   // segmentation fault.
   if (ctx.reldyn && ctx.arg.is_static && !ctx.arg.pie) {
-    start(ctx.__rel_iplt_start, ctx.reldyn);
+    stop(ctx.__rel_iplt_start, ctx.reldyn);
+    stop(ctx.__rel_iplt_end, ctx.reldyn);
 
-    ctx.__rel_iplt_end->shndx = -ctx.reldyn->shndx;
-    ctx.__rel_iplt_end->value = ctx.reldyn->shdr.sh_addr +
+    ctx.__rel_iplt_start->value -=
       get_num_irelative_relocs(ctx) * sizeof(ElfRel<E>);
   }