[LCG] Replace an implicit bool operator with a named function. (NFC)

[LCG] Replace an implicit bool operator with a named function. (NFC)

The definition of 'false' here was already pretty vague and debatable,
and I'm about to add another potential 'false' that would actually make
much more sense in a bool operator. Especially given how rarely this is
used, a nicely named method seems better.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310165 91177308-0d34-0410-b5e6-96231b3b80d8