Prefer not to break after assignments.

This addresses llvm.org/PR14830.

Before:
unsigned Cost =
    TTI.getMemoryOpCost(I->getOpcode(), VectorTy, SI->getAlignment(),
                        SI->getPointerAddressSpace());
CharSourceRange LineRange =
    CharSourceRange::getTokenRange(TheLine.Tokens.front().Tok.getLocation(),
                                   TheLine.Tokens.back().Tok.getLocation());

After:
unsigned Cost = TTI.getMemoryOpCost(I->getOpcode(), VectorTy,
                                    SI->getAlignment(),
                                    SI->getPointerAddressSpace());
CharSourceRange LineRange = CharSourceRange::getTokenRange(
                                TheLine.Tokens.front().Tok.getLocation(),
                                TheLine.Tokens.back().Tok.getLocation());

This required rudimentary changes to static initializer lists, but we
are not yet formatting them in a reasonable way. That will be done in a
subsequent patch.