libc/glibc: set the float option according to extra CFLAGS

When building a multilib, some extra CFLAGS can override the
default config option. This is the case for the floating point
selection.

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

 reporter_name="Bart vdr. Meulen <bartvdrmeulen@gmail.com>"

 reporter_url=""

 reporter_comment="Config to build cross-compiler with mingw as kernel type"