softfloat: Replace countLeadingZeros32/64 with clz32/64

softfloat: Replace countLeadingZeros32/64 with clz32/64

Our minimum required compiler for compiling QEMU is GCC 4.1 these days,
so we can drop the support for compilers which do not provide the
__builtin_clz*() functions yet. Since the countLeadingZeros32/64 are
then identical to the clz32/64 functions, and we do not have to sync
the softloat 2 codebase with upstream anymore (softloat 3 is a complete
rewrite) we can simply replace the functions with our QEMU versions.

Suggested-by: Peter Maydell <[email protected]>
Acked-by: Alex Bennée <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>
Message-Id: <1538118095[email protected]>
Signed-off-by: Richard Henderson <[email protected]>