[lld] [lld][ELF][AVR] Add range check for R_AVR_13_PCREL (PR #67636)

[via llvm-commits]

aykevl wrote:

The change to `R_AVR_7_PCREL` broke linking when updating to LLVM 18:

```
ld.lld-18: error: /tmp/tinygo1961037610/main.lto.main.o:(function runtime.run$1$gowrapper: .text.runtime.run$1$gowrapper+0x4c0): relocation R_AVR_7_PCREL out of range: -66 is not in [-64, 63]; references section '.text.runtime.run$1$gowrapper'
```

When I undo that one line change using the following patch, all AVR tests pass:

```diff
   case R_AVR_7_PCREL: {
-    checkInt(loc, val - 2, 7, rel);
+    checkInt(loc, val, 7, rel);
     checkAlignment(loc, val, 2, rel);
     const uint16_t target = (val - 2) >> 1;
     write16le(loc, (read16le(loc) & 0xfc07) | ((target & 0x7f) << 3));
     break;
   }
```

https://github.com/llvm/llvm-project/pull/67636