[Clang][Driver] Fix `--save-temps` for OpenCL AoT compilation (#78333)

We can directly call `clang -c -x cl -target amdgcn -mcpu=gfx90a test.cl
-o test.o`
to compile an OpenCL kernel file. However, when `--save-temps` is
enabled, it doesn't
work because the preprocessed file (`.i` file) is taken as C source file
when it
is fed to the front end, thus causing compilation error because those
OpenCL keywords
can't be recognized. This patch fixes the issue.