lib/CWriter/Writer.cpp: Copy AsmWriter's ConstantFP checking code here

into a new function FPCSafeToPrint(), and use it in printConstant()
and printFunction() to decide whether we should output ConstantFPs as
floating-point constants or as references to stack-allocated variables.

lib/VMCore/AsmWriter.cpp: Fix an apparent typo in the code mentioned above.

llvm-svn: 6762