This patch generates a warning for invalid combination of '-mnan' and
'-march' options, it properly sets NaN encoding for a given '-march',
and it passes a proper NaN encoding to the assembler.

Patch by Vladimir Radosavljevic.

Differential Revision: http://reviews.llvm.org/D8170


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234882 91177308-0d34-0410-b5e6-96231b3b80d8