When attribute 'optnone' appears on the same declaration with a

conflicting attribute, warn about the conflict and pick a "winning"
attribute to preserve, instead of emitting an error.  This matches the
behavior when the conflicting attributes are on different declarations.

Along the way I discovered that conflicts involving __forceinline were
reported as 'always_inline' (alternate spelling, same attribute) so
fixed that up to report the attribute as spelled in the source.

llvm-svn: 225813