Add support to cuda c file

[changephilip]

My project includes some .cu and .cuh files.
Cquery server can't find these files even i had wrote file path in .cquery file.
The server will report error like below:
"
Error from the Language Server: Unable to find file /xxx/xxx/xx/xxx.cuh.(Internal Error)
"

[bstaletic]

This isn't too easy, but isn't too hard either.
Here's how ycmd implemented it: ycm-core/ycmd#1031
Clang can compile cuda projects, but if the compilation database is made with nvcc, there's going to be trouble. Read everything in the above link for details.

[Kelvin-Ng]

Does it mean that it is easy if .cquery is used, or the compilation database is not made with nvcc?

[bstaletic]

Yes, because it eliminates the known not working configuration. Someone still has to make sure cquery isn't doing anything stupid and write tests that prove that cuda works.

[Kelvin-Ng]

I have made some minor changes to make it work with CUDA using .cquery. I am currently using it to write CUDA programs. It works great so far. I will see if there is any problem after longer usage.