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>

 # SPARC specific config options

 ## select ARCH_SUPPORTS_32

 ## select ARCH_SUPPORTS_64

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ##

 ## help The SUN SPARC architecture, as defined by:

 ## help     32 bit: http://www.sparc.org/standards/V8.pdf

 ## help     64 bit: http://www.sparc.org/standards/SPARCV9.pdf