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>

 # Menu for the native GDB

 config GDB_NATIVE

     bool

     prompt "Native gdb"

     depends on ! BARE_METAL

     depends on ! BACKEND

     help

       Build and install a native gdb for the target, to run on the target.

 if GDB_NATIVE

 config GDB_NATIVE_STATIC

     bool

     prompt "Build a static native gdb"

     help

       In case you have trouble with dynamic loading of shared libraries,

       you will find that a static gdb comes in handy.

 endif # GDB_NATIVE