Don't use std::__clz in 'test/support/hexfloat.h'.
Don't use std::__clz in 'test/support/hexfloat.h'.

std::__clz is a libc++ specific function so it can't be used in the test suite.
This patch implements a dumb "count leading zeros" implementation within
hexfloat itself.

This patch also fixes UB since the output of `__builtin_clz(0)` is undefined
according to the GCC docs.


git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@268354 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx