Fix libfloat when calling the compiler:
- when not compiling NPTL, the shared core C compiler does not exist,
- PATH arranges for the shared core C compiler to be found before the static one, so no need to force it.

 source config/global.in

 source config/target.in

 source config/toolchain.in

 source config/kernel.in

 source config/binutils.in

 source config/cc.in

 source config/libc.in

 source config/debug.in