message: guix: no-longer pass --enable-glibc-back-compat to Guix
  Now that our Guix builds are performed on glibc 2.24 and 2.27 (RISCV),
  we no-longer need to pass the --enable-glibc-back-compat option.
  Replace it with --disable-threadlocal, to prevent the usage of symbols
  from glibc 2.18.
  None of the binaries produced required symbols later than 2.17, and 2.27
  (RISCV).
diff: @@ -240,7 +240,7 @@ mkdir -p "$OUTDIR"
  # CONFIGFLAGS
  CONFIGFLAGS="--enable-reduce-exports --disable-bench --disable-gui-tests --disable-fuzz-binary"
  case "$HOST" in
  - *linux*) CONFIGFLAGS+=" --enable-glibc-back-compat" ;;
  + *linux*) CONFIGFLAGS+=" --disable-threadlocal" ;;
  esac
  # CFLAGS
  @@ -260,6 +260,13 @@ case "$HOST" in
  *mingw*) HOST_LDFLAGS="-Wl,--no-insert-timestamp" ;;
  esac
  +# Using --no-tls-get-addr-optimize retains compatibility with glibc 2.17, by
  +# avoiding a PowerPC64 optimisation available in glibc 2.22 and later.
  +# https://sourceware.org/binutils/docs-2.35/ld/PowerPC64-ELF64.html
  +case "$HOST" in
  + *powerpc64*) HOST_LDFLAGS="${HOST_LDFLAGS} -Wl,--no-tls-get-addr-optimize" ;;
  +esac
  +
  case "$HOST" in
  powerpc64-linux-*|riscv64-linux-*) HOST_LDFLAGS="${HOST_LDFLAGS} -Wl,-z,noexecstack" ;;
  esac
  