A complimentary change to D85548. This change allows strict_fsub x, (fneg y) to become strict_fadd x, y while preserving chain ordering outside of these operations.
A number of tests were changed significantly because DAGCombiner optimizations cannot be disabled.
clang-tidy: warning: invalid case style for function 'visitSTRICT_FSUB' [readability-identifier-naming]
not useful