scripts: Use ninja.exe on Windows if present in PATH

Visual Studio 2019 ships with ninja.exe.

Author: thewtex

scripts/internal/windows_build_common.py

@@ -2,6 +2,7 @@
 
 from subprocess import check_call
 import os
+import shutil
 
 DEFAULT_PY_ENVS = ["35-x64", "36-x64", "37-x64", "38-x64"]
 
@@ -32,6 +33,8 @@ def venv_paths(python_version):
     pip = os.path.join(venv_dir, "Scripts", "pip.exe")
 
     ninja_executable = os.path.join(venv_dir, "Scripts", "ninja.exe")
+    if not os.path.exists(ninja_executable):
+        ninja_executable = shutil.which("ninja.exe")
     print("NINJA_EXECUTABLE:%s" % ninja_executable)
 
     # Update PATH

scripts/windows_build_wheels.py

@@ -251,8 +251,10 @@ def build_wheels(py_envs=DEFAULT_PY_ENVS, single_wheel=False,
 
         cmake_executable = "cmake.exe"
         tools_venv = os.path.join(ROOT_DIR, "venv-" + py_envs[0])
-        pip_install(tools_venv, "ninja")
-        ninja_executable = os.path.join(tools_venv, "Scripts", "ninja.exe")
+        ninja_executable = shutil.which('ninja.exe')
+        if ninja_executable is None:
+            pip_install(tools_venv, "ninja")
+            ninja_executable = os.path.join(tools_venv, "Scripts", "ninja.exe")
 
         # Build standalone project and populate archive cache
         check_call([
@@ -268,7 +270,9 @@ def build_wheels(py_envs=DEFAULT_PY_ENVS, single_wheel=False,
     # Compile wheels re-using standalone project and archive cache
     for py_env in py_envs:
         tools_venv = os.path.join(ROOT_DIR, "venv-" + py_env)
-        pip_install(tools_venv, "ninja")
+        ninja_executable = shutil.which('ninja.exe')
+        if ninja_executable is None:
+            pip_install(tools_venv, "ninja")
         build_wheel(py_env, single_wheel=single_wheel,
             cleanup=cleanup, wheel_names=wheel_names,
             cmake_options=cmake_options)