tools/elfutils: add missing MIPS reloc support

tools/elfutils: add missing MIPS reloc support

Backport an upstream patch series that adds backend elfutils support for
DWARF relocations in MIPS debug info. This support is needed by pahole to
generate BTF for modules in BTF-enabled kernel builds.

The problem first manifests as pahole warnings during build:

    BTF [M] lib/libcrc32c.ko
    die__process_unit: DW_TAG_compile_unit (0x11) @ <0x932d> not handled!
    die__process_unit: tag not supported 0x11 (compile_unit)!
    die__process: got compile_unit unexpected tag after DW_TAG_compile_unit!
    die__process_unit: DW_TAG_compile_unit (0x11) @ <0x99a3> not handled!
    die__process_unit: tag not supported 0x11 (compile_unit)!
    die__process: got compile_unit unexpected tag after DW_TAG_compile_unit!

During system boot the problem then causes module loading failures, which
may result in many other runtime issues:

    [   13.169785] kmodloader: loading kernel modules from /etc/modules.d/*
    [ ... ]
    [   17.422840] mac80211_hwsim: initializing netlink
    [   17.526518] PPP generic driver version 2.4.2
    [   17.550346] NET: Registered PF_PPPOX protocol family
    [   17.795353] kmodloader: 26 modules could not be probed
    [   17.796084] kmodloader: dependency not loaded nf_conntrack
    [   17.796737] kmodloader: - act_connmark - 1
    [   17.797402] kmodloader: dependency not loaded nf_conntrack
    [   17.798056] kmodloader: - act_ctinfo - 1
    [ ... ]

Link: https://lore.kernel.org/bpf/ZlkoM6%2FPSxVcGM6X@kodidev-ubuntu/
Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
Link: https://github.com/openwrt/openwrt/pull/15697
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>