Revert 266186 as it breaks anything that includes type_traits on some platforms

Since this patch provided support for the __float128 type but disabled it
on all platforms by default, some platforms can't compile type_traits with
-std=gnu++11 since there is a specialization with __float128.
This reverts the patch until D19125 is approved (i.e. we know which platforms
need this support enabled).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266460 91177308-0d34-0410-b5e6-96231b3b80d8