bpo-34267: Update find_python.bat to use 3.7 if available (GH-8552)

PCbuild/find_python.bat

@@ -34,7 +34,7 @@
 @if NOT "%HOST_PYTHON%"=="" @%HOST_PYTHON% -Ec "import sys; assert sys.version_info[:2] >= (3, 6)" >nul 2>nul && (set PYTHON="%HOST_PYTHON%") && (set _Py_Python_Source=found as HOST_PYTHON) && goto :found
 
 @rem If py.exe finds a recent enough version, use that one
-@py -3.6 -EV >nul 2>&1 && (set PYTHON=py -3.6) && (set _Py_Python_Source=found with py.exe) && goto :found
+@for %%p in (3.7 3.6) do @py -%%p -EV >nul 2>&1 && (set PYTHON=py -%%p) && (set _Py_Python_Source=found %%p with py.exe) && goto :found
 
 @if NOT exist "%_Py_EXTERNALS_DIR%" mkdir "%_Py_EXTERNALS_DIR%"
 @set _Py_NUGET=%NUGET%
@@ -55,7 +55,7 @@
 )
 @echo Installing Python via nuget...
 @"%_Py_NUGET%" install pythonx86 -ExcludeVersion -OutputDirectory "%_Py_EXTERNALS_DIR%"
-@rem Quote it here; it's not quoted later because "py -3.6" wouldn't work
+@rem Quote it here; it's not quoted later because "py -x.y" wouldn't work
 @if not errorlevel 1 (set PYTHON="%_Py_EXTERNALS_DIR%\pythonx86\tools\python.exe") & (set _Py_Python_Source=found on nuget.org) & goto :found