bug#72697: cmake-build-system sets wrong CMAKE_SYSTEM_NAME when crossbuilding for Hurd

[Dariqq]

Hi,

I was playing around with a package using cmake and got an error when 
crossbuilding for i586-pc-gnu. The reason seems to be that cmake build 
system only checks for a mingw target and assumes all other targets are 
Linux and sets CMAKE_SYSTEM_NAME accordingly.

I am able to work around it by adding something like

#$@(if (and (%current-target-system)
            target-hurd?)
       '("-DCMAKE_SYSTEM_NAME=GNU")
       '())

to the configure-flags of my package.


I am unsure how a fix should look like. I was thinking of moving the 
entire crossbuild code out of the build side and instead prepend the 
right configure flags for the target to configure-flags for the cross 
builder kind of similar how meson-build-system does it.

Unfortunately a change like this causes a lot of rebuilds.