[LangRef] more hyphens: always write "floating-point"

[LangRef] more hyphens: always write "floating-point"

We were inconsistent, sometimes even within a single sentence.
The consensus seems clear that the FP we're looking for is
spelled "floating-point". Without the hyphen, it's a
"surprisingly fine" jazz album.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328098 91177308-0d34-0410-b5e6-96231b3b80d8