The number of Christians martyred by Islam is 9 million [David B. Barrett, Todd M. Johnson, World Christian Trends AD 30-AD 2200, William Carey Library, 2001, p. 230, table 4-10] .
A rough estimate by Raphael Moore in History of Asia Minor is that another 50 million died in wars by jihad.
So counting the million African Christians killed in the 20th century we have:
60 million Christians
[This calculation does not include the Arab biological warfare of the middle ages where enslaved and infected Jews, riddled with plague, were dumped across Europe in regions that had no Jewish origin or settlers. They carried the disease from the brutal Arab slave trade and were part of the enslaved blacks, Christians and Jews who managed to survive by paying jizya. These diseased people were then spread into Europe during muslim efforts to conquer the Italian coast (Venice), Greece, Spain, etc. The plague ended up killing half of the entire population of Europe]