nix: mark nocross.

Commit 51c4b1859a removed the libcpuid
dependency, which enabled the build for ARM archs, despite the package
not having been tested there. The current template is not ready for
cross compilation.

The build initially failed with:

     LD     /usr/lib32/libnixstore.so
   [cc-wrapper] ignoring -L/usr/lib32
   /usr/lib/gcc/armv7l-linux-musleabihf/10.2.1/../../../../armv7l-linux-musleabihf/bin/ld: cannot find -lnixutil

because the libinixutil.so file was located in /usr/lib32 of the
masterdir, which should never have happened. Bypassing that error also
leads us to:

     LD     /usr/lib32/libnixexpr.so
   /usr/lib/gcc/armv7l-linux-musleabihf/10.2.1/../../../../armv7l-linux-musleabihf/bin/ld: cannot find -latomic_ops

meaning the build requires further fixes for armv*, probably beyond
cross compilation.

Still add jq to hostmakedepends, since the build requires the jq binary
as well.

srcpkgs/nix/template

@@ -5,7 +5,7 @@ revision=1
 build_style=gnu-configure
 # Use /nix/var as suggested by the official Manual.
 configure_args="--localstatedir=/nix/var --with-sandbox-shell=/bin/sh"
-hostmakedepends="curl pkg-config flex tar xz automake autoconf-archive mdBook"
+hostmakedepends="curl pkg-config flex tar xz automake autoconf-archive mdBook jq"
 makedepends="boost-devel brotli-devel bzip2-devel gc-devel libcurl-devel
  liblzma-devel openssl-devel libsodium-devel sqlite-devel
  libseccomp-devel editline-devel jq-devel libarchive-devel
@@ -19,6 +19,7 @@ changelog="https://nixos.org/releases/${pkgname}/${pkgname}-${version}/manual/#s
 distfiles="https://github.com/NixOS/nix/archive/refs/tags/${version}.tar.gz"
 checksum=91a7f2bcdde3263927d842f04a345ed77319148c700e2c8be01498724e6808c0
 disable_parallel_build=yes
+nocross="cross build populates /usr/lib32 with libraries and tries to link against them"
 
 if [ "$XBPS_TARGET_LIBC" = "musl" ]; then
 	makedepends+=" musl-legacy-compat"