x86: detect unsupported relocation types

Currently we support only relocations of type ELF64_R_TYPE or ELF32_R_TYPE.
We should be warned if other relocation types appear in the relocation
sections.

This type of message has helped to identify code overwriting a relocation
section before relocation and incorrect parsing of relocation tables.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>