Fix extension rebuilding on Linux (#108613)
On Linux, CUDA header dependencies are not correctly tracked. After you modify a CUDA header, affected CUDA files won't be rebuilt. This PR will fix this problem.
```console
$ ninja -t deps
rep_penalty.o: #deps 2, deps mtime 1693956351892493247 (VALID)
/home/qc/Workspace/NotMe/exllama/exllama_ext/cpu_func/rep_penalty.cpp
/home/qc/Workspace/NotMe/exllama/exllama_ext/cpu_func/rep_penalty.h
rms_norm.cuda.o: #deps 0, deps mtime 1693961188871054130 (VALID)
rope.cuda.o: #deps 0, deps mtime 1693961188954388632 (VALID)
cuda_buffers.cuda.o: #deps 0, deps mtime 1693961188797719768 (VALID)
...
```
Historically, this line of code has been changed twice. It was first implemented in #49344 and there's no `if IS_WINDOWS`, just like now. Then in #56015 someone added `if IS_WINDOWS` for unknown reason. That PR has no description so I don't know what bug he encountered. I don't think there's any bug with these flags on Linux, at least for today. CMake generates exactly the same flags for CUDA.
```ninja
#############################################
# Rule for compiling CUDA files.
rule CUDA_COMPILER__cpp_cuda_unscanned_Debug
depfile = $DEP_FILE
deps = gcc
command = ${LAUNCHER}${CODE_CHECK}/opt/cuda/bin/nvcc -forward-unknown-to-host-compiler $DEFINES $INCLUDES $FLAGS -MD -MT $out -MF $DEP_FILE -x cu -c $in -o $out
description = Building CUDA object $out
```
where `-MD` is short for `--generate-dependencies-with-compile` and `-MF` is short for `--dependency-output`. My words can be verified by `nvcc --help`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108613
Approved by: https://github.com/ezyang
