bpo-45402: Fix test_tools.test_sundry() (GH-28786)

Fix test_tools.test_sundry() when Python is built out of tree: fix
how the freeze_modules.py tool locates the _freeze_module program.

Author: vstinner

Misc/NEWS.d/next/Tests/2021-10-07-13-43-01.bpo-45402.jlQvep.rst

@@ -0,0 +1,3 @@
+Fix test_tools.test_sundry() when Python is built out of tree: fix how
+the freeze_modules.py tool locates the _freeze_module program.
+Patch by Victor Stinner.

Tools/scripts/freeze_modules.py

@@ -29,9 +29,10 @@
 if sys.platform != "win32":
     TOOL = os.path.join(ROOT_DIR, 'Programs', '_freeze_module')
     if not os.path.isfile(TOOL):
-        # When building out of the source tree, get the tool from the current
-        # directory
-        TOOL = os.path.join('Programs', '_freeze_module')
+        # When building out of the source tree, get the tool from directory
+        # of the Python executable
+        TOOL = os.path.dirname(sys.executable)
+        TOOL = os.path.join(TOOL, 'Programs', '_freeze_module')
         TOOL = os.path.abspath(TOOL)
         if not os.path.isfile(TOOL):
             sys.exit("ERROR: missing _freeze_module")