fix bug that resolved and unsolved conflict

Signed-off-by: xiehuc <xiehuc@gmail.com>
add ddg.cpp

Signed-off-by: xiehuc <xiehuc@gmail.com>
rename DDG as DDGraph

Signed-off-by: xiehuc <xiehuc@gmail.com>
add DOTTraits for ddg

Signed-off-by: xiehuc <xiehuc@gmail.com>