link.Elf: allow multiple relocs at the same location

RISC-V and LoongArch ELF psABIs define a kind of
RELAX relocations which are expected to have a normal
relocation at the same address.

Change-Id: I5737bfcfd3e5041fb6ab7d193c9fc57eeca1eec8

src/link/Elf/relocatable.zig

@@ -383,7 +383,6 @@ fn writeSyntheticSections(elf_file: *Elf) !void {
     const SortRelocs = struct {
         pub fn lessThan(ctx: void, lhs: elf.Elf64_Rela, rhs: elf.Elf64_Rela) bool {
             _ = ctx;
-            assert(lhs.r_offset != rhs.r_offset);
             return lhs.r_offset < rhs.r_offset;
         }
     };