Make build-system more cross-compilation friendly.
loader: Don't embed "build-id" section, it might conflict with loaded programs.

On Fedora, Debian, Ubuntu, and likely on many other distros, a
loadable segment is automatically added by the linker:

    The new section is canonically called .note.gnu.build-id [... it]
    has SHF_ALLOC in sh_flags, meaning it appears in the loaded memory
    image, and the normal link order puts allocated note sections very
    early in the memory image.

    -- https://fedoraproject.org/wiki/Releases/FeatureBuildId

By default this segment is mapped to a low address:

    $ readelf -lW src/loader/loader
    [...]
    Program Headers:
      Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
      LOAD           0x000000 0x0000000000400000 0x0000000000400000 0x000144 0x000144 R   0x200000
      LOAD           0x200000 0x0000600000000000 0x0000600000000000 0x000388 0x000388 R E 0x200000
      NOTE           0x000120 0x0000000000400120 0x0000000000400120 0x000024 0x000024 R   0x4
      GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RWE 0x10

     Section to Segment mapping:
      Segment Sections...
       00     .note.gnu.build-id
       01     .text .rodata .eh_frame
       02     .note.gnu.build-id
       03

As a consequence, this unexpected segment in the loader might conflict
with PRooted processes:

    $ proot -q qemu-sh4 -r stlinux-2.4-sh4/ /bin/sh -c 'true; id'
    [...]
    qemu: uncaught target signal 11 (Segmentation fault) - core dumped

Reported-by: Jerome AUDU <jerome.audu@st.com>