Capture stderr when creating the virtualenv to see if it adds any extra info

Author: dconeybe

cmake/external/firestore_snappy.patch.txt

@@ -887,3 +887,29 @@ index 000000000..bdb7b9f6a
 +
 +  set("${ARG_OUTVAR}" "${PYTHON_EXECUTABLE}" PARENT_SCOPE)
 +endfunction(FirebaseSetupPythonInterpreter)
+diff --git a/cmake/python_setup.cmake b/cmake/python_setup.cmake
+index bdb7b9f6a..ebce71d96 100644
+--- a/cmake/python_setup.cmake
++++ b/cmake/python_setup.cmake
+@@ -1,4 +1,4 @@
+-# Copyright 2022 Google LLC
++
+ #
+ # Licensed under the Apache License, Version 2.0 (the "License");
+ # you may not use this file except in compliance with the License.
+@@ -128,11 +128,14 @@ function(FirebaseSetupPythonInterpreter)
+       "${PYVENV_DIRECTORY}"
+     RESULT_VARIABLE
+       FIREBASE_PYVENV_CREATE_RESULT
++    ERROR_VARIABLE
++      FIREBASE_PYVENV_CREATE_ERROR
++    ERROR_STRIP_TRAILING_WHITESPACE
+   )
+   if(NOT FIREBASE_PYVENV_CREATE_RESULT EQUAL 0)
+     message(FATAL_ERROR
+       "Failed to create a Python virtualenv in ${PYVENV_DIRECTORY} "
+-      "using ${FIREBASE_PYTHON_HOST_EXECUTABLE}")
++      "using ${FIREBASE_PYTHON_HOST_EXECUTABLE}: ${FIREBASE_PYVENV_CREATE_ERROR}")
+   endif()
+ 
+   # Find the Python interpreter in the virtualenv.