Fix the return type of the complex creal functions. Patch by YunZhong Gao, modified to use _Static_assert and to check __STDC_HOSTED__ by me.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181527 91177308-0d34-0410-b5e6-96231b3b80d8