[ELF] Don't create copy relocation/canonical PLT entry for a defined symbol (#75095)

Copy relocations and canonical PLT entries are for symbols defined in a
DSO. Currently we create them even for a `Defined`, possibly leading to
an output that won't work at run-time (e.g. R_X86_64_JUMP_SLOT
referencing a null symbol).
```
% cat a.s
.globl _start, main
.type main, @function
_start: main: ret

.rodata
.quad main
% clang -fuse-ld=lld -pie -nostdlib a.s
% readelf -Wr a.out

Relocation section '.rela.plt' at offset 0x290 contains 1 entry:
    Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
00000000000033b8  0000000000000007 R_X86_64_JUMP_SLOT                        12b0
```

Report an error instead for the default `-z text` mode. GNU ld reports
an error in `-z text` mode as well.