Currently the two flags can not work together.
To illustrate the issue, we can have an one line file a.cl contains only an empty function
clang -v -save-temps -x cl -Xclang -cl-std=CL2.0 -Xclang -finclude-default-header -target amdgcn -S -c a.cl
we will get redefinition errors for various things.
The reason is that the -finclude-default-header flag is not meant to be on cc1 command other than the preprocessor.
The fix is modeled after the code just below the change to filter the -finclude-default-header flag out when we are not in the preprocess phase.