Restore getpath.c closer to upstream

Instead of changing the control flow significantly, use SetPythonHome,
-DPYTHONPATH, and a handful of ifdefs.

Test: build/soong/python/tests/runtest.sh
Test: git diff 18e21883a4..HEAD -- Modules/getpath.c
Change-Id: I27ca46f953c160e437b1610085cc756056ba3812
diff --git a/Android.bp b/Android.bp
index 2a56885..5d72eda 100644
--- a/Android.bp
+++ b/Android.bp
@@ -219,7 +219,10 @@
         "-DVPATH=\"\"",
         "-DPREFIX=\"\"",
         "-DEXEC_PREFIX=\"\"",
-        "-DPYTHONPATH=\"\"",
+        "-DPYTHONPATH=\"..:\"",
+        "-DANDROID_SKIP_ZIP_PATH",
+        "-DANDROID_SKIP_EXEC_PREFIX_PATH",
+        "-DANDROID_LIB_PYTHON_PATH=\"internal/stdlib\"",
         "-DDATE=\"Dec 31 1969\"",
         "-DTIME=\"23:59:59\"",
     ],