[ELF][RISCV] Handle R_RISCV_FUNC_RELATIVE in getImplicitAddend

Otherwise linking with --apply-dynamic-relocs (as is done by U-Boot, or
due to -z rel which we don't support) when --check-dynamic-relocs is
enabled (which is the default in assertions builds) will give an
internal linker error when such a relocation is emitted.

Fixes: 2d52aa8 ("[ELF][RISCV] Support R_RISCV_CHERI_CAPABILITY_CODE and R_RISCV_FUNC_RELATIVE")

Author: dpgao

lld/ELF/Arch/RISCV.cpp

@@ -225,6 +225,7 @@ int64_t RISCV::getImplicitAddend(const uint8_t *buf, RelType type) const {
     return read64le(buf);
   case R_RISCV_RELATIVE:
   case R_RISCV_IRELATIVE:
+  case R_RISCV_FUNC_RELATIVE:
     return ctx.arg.is64 ? read64le(buf) : read32le(buf);
   case R_RISCV_NONE:
   case R_RISCV_JUMP_SLOT: