I'm trying to build a guix system for my banana pi m2u, but json-c fails 
to cross-build.

~$ guix describe
Generation 319    Nov 04 2020 06:41:25    (current)
   guix 3d67269
     repository URL: https://git.savannah.gnu.org/git/guix.git
     branch: master
     commit: 3d67269ee787c8624bafdd68df9fbf7eedd8eb1e

~$ guix build --system=armhf-linux json-c
...
command "cmake" "../json-c-0.14" "-DCMAKE_BUILD_TYPE=RelWithDebInfo" 
"-DCMAKE_INSTALL_PREFIX=/gnu/store/yqaw63n8wmg7f2ncc24019z87m5cwhim-json-c-0.14" 
"-DCMAKE_INSTALL_LIBDIR=lib" "-DCMAKE_INSTALL_RPATH_USE_LINK_PATH=TRUE" 
"-DCMAKE_INSTALL_RPATH=/gnu/store/yqaw63n8wmg7f2ncc24019z87m5cwhim-json-c-0.14/lib" 
"-DCMAKE_VERBOSE_MAKEFILE=ON" failed with status 1
builder for 
`/gnu/store/m3x5hnlp9d9qmg72a0c7rqlz40yc0x0m-json-c-0.14.drv' failed 
with exit code 1
build of /gnu/store/m3x5hnlp9d9qmg72a0c7rqlz40yc0x0m-json-c-0.14.drv failed
View build log at 
'/var/log/guix/drvs/m3/x5hnlp9d9qmg72a0c7rqlz40yc0x0m-json-c-0.14.drv.bz2'.
guix build: error: build of 
`/gnu/store/m3x5hnlp9d9qmg72a0c7rqlz40yc0x0m-json-c-0.14.drv' failed


Log attached.