setup correct nvcc version with CUDA_HOME (#15725)

Signed-off-by: Yang Chen <yangche@fb.com>

setup.py

@@ -201,6 +201,9 @@ class cmake_build_ext(build_ext):
         else:
             # Default build tool to whatever cmake picks.
             build_tool = []
+        # Make sure we use the nvcc from CUDA_HOME
+        if _is_cuda():
+            cmake_args += [f'-DCMAKE_CUDA_COMPILER={CUDA_HOME}/bin/nvcc']
         subprocess.check_call(
             ['cmake', ext.cmake_lists_dir, *build_tool, *cmake_args],
             cwd=self.build_temp)
@@ -639,11 +642,10 @@ if _is_hip():
 
 if _is_cuda():
     ext_modules.append(CMakeExtension(name="vllm.vllm_flash_attn._vllm_fa2_C"))
-    if envs.VLLM_USE_PRECOMPILED or get_nvcc_cuda_version() >= Version("12.0"):
-        # FA3 requires CUDA 12.0 or later
+    if envs.VLLM_USE_PRECOMPILED or get_nvcc_cuda_version() >= Version("12.3"):
+        # FA3 requires CUDA 12.3 or later
         ext_modules.append(
             CMakeExtension(name="vllm.vllm_flash_attn._vllm_fa3_C"))
-    if envs.VLLM_USE_PRECOMPILED or get_nvcc_cuda_version() >= Version("12.3"):
         # Optional since this doesn't get built (produce an .so file) when
         # not targeting a hopper system
         ext_modules.append(