replace distutils.spawn with shutil.which per PEP632 in setup script (#5849)

Co-authored-by: Bruno Korbar <bkorbar@quansight.com>
Co-authored-by: Nicolas Hug <contact@nicolas-hug.com>

setup.py

@@ -102,7 +102,7 @@ def find_library(name, vision_include):
             conda_installed = library_found
         else:
             # Check if using Anaconda to produce wheels
-            conda = distutils.spawn.find_executable("conda")
+            conda = shutil.which("conda")
             is_conda = conda is not None
             print(f"Running build on conda: {is_conda}")
             if is_conda:
@@ -259,8 +259,8 @@ def get_extensions():
         image_macros += [("USE_PYTHON", None)]
 
     # Locating libPNG
-    libpng = distutils.spawn.find_executable("libpng-config")
-    pngfix = distutils.spawn.find_executable("pngfix")
+    libpng = shutil.which("libpng-config")
+    pngfix = shutil.which("pngfix")
     png_found = libpng is not None or pngfix is not None
     print(f"PNG found: {png_found}")
     if png_found:
@@ -340,7 +340,7 @@ def get_extensions():
             )
         )
 
-    ffmpeg_exe = distutils.spawn.find_executable("ffmpeg")
+    ffmpeg_exe = shutil.which("ffmpeg")
     has_ffmpeg = ffmpeg_exe is not None
     # FIXME: Building torchvision with ffmpeg on MacOS or with Python 3.9
     # FIXME: causes crash. See the following GitHub issues for more details.
@@ -366,7 +366,7 @@ def get_extensions():
         ffmpeg_include_dir = os.path.join(ffmpeg_root, "include")
         ffmpeg_library_dir = os.path.join(ffmpeg_root, "lib")
 
-        gcc = os.environ.get("CC", distutils.spawn.find_executable("gcc"))
+        gcc = os.environ.get("CC", shutil.which("gcc"))
         platform_tag = subprocess.run([gcc, "-print-multiarch"], stdout=subprocess.PIPE)
         platform_tag = platform_tag.stdout.strip().decode("utf-8")