ld: support --build-id=xx mode

ld: support --build-id=xx mode

The is patch adds a new ld build-id computation mode, "xx", using
xxhash in its 128-bit mode.  The patch prereqs the xxhash-devel
headers being installed, and uses the "all-inlined" model, so no
run-time or link-time library dependence exists.

The xxhash mode performs well, saving roughly 20% of total userspace
run time from an ld job over a 800MB shared library relative to sha1.
128 bits of good hash should be collision-resistant to a number of
distinct binaries that numbers in the 2**32 - 2**64 range, even if not
"crypto" level hash.  Confirmations of this are in progress.

         ld/configury: add --with-xxhash mode, different from gdb case
                       because only using it in inline mode

         ld/ldbuildid.c: add "xx" mode, #if WITH_XXHASH

         ld/NEWS, ld.texi: mention new option

         ld/lexsup.c: add enumeration of --build-id STYLES to --help

         ld/testsuite/ld-elf/build-id.exp: add test case for 0xHEX case
                                           and conditional for xx case;
                                           also, simply tcl list syntax

https://inbox.sourceware.org/binutils/20240917201509.GB26396@redhat.com/

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>