scripts: check host features with host compiler

Currently, we check host feature in ./configure. This works only for
cross toolchains, but not for canadian toolchains. ./configure has
absolutely no way to know what the host for the toolchain will be;
only the build scripts know.

So, move the headers & libraries checks from ./configure to the build
scripts, early enough in the build, but not before we know the host
compiler and other tools.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # s390 specific config options

 ## depends on EXPERIMENTAL

 ##

 ## select ARCH_SUPPORTS_32

 ## select ARCH_SUPPORTS_64

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORT_FPU

 ##

 ## help Defined by IBM in:

 ## help     32-bit ESA/390       : http://publibfp.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/dz9ar008/CCONTENTS

 ## help     64-bit z/Architecure : http://publibfp.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/dz9zr002/CCONTENTS