AsmParser: test .double NaN and .double inf
Summary: It looks like this support was added to match GNU AS, but only tests
.float and not .double. I asked RedHat folks to confirm that 0x7fffffffffffffff
was indeed the right value for NaN.
Same for infinity, but it only has positive / negative encodings.
Reviewers: scanon, rjmccall
Subscribers: jkorous, dexonsmith, llvm-commits
Differential Revision: https://reviews.llvm.org/D55531