layout: restructure into src/ tests/ android/ scripts/ tools/

- extension/src/{port,platform,codepage} -> src/; native_render -> src/host
  (+ dxt, shaders/); libgr2 -> src/gr2; extension/third_party -> third_party
- extension/tests -> tests/port, libgr2/tests -> tests/gr2
- android-native -> android (build.sh, push-client.sh moved in)
- script -> scripts; tools/40250 -> tools/server; oracle -> tools/granny-oracle;
  perf tools -> tools/perf
- all build trees under build/ (native, release, android, port-gate)
- xrender:: CMake aliases -> mt::; port-map ledger impl paths rewritten

No code changes. ctest 15/15, port_gate macos+android PASS, port_map check 0 errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

third_party/cpython-2.7.18/Python/sigcheck.c

@@ -0,0 +1,19 @@
+
+/* Sigcheck is similar to intrcheck() but sets an exception when an
+   interrupt occurs.  It can't be in the intrcheck.c file since that
+   file (and the whole directory it is in) doesn't know about objects
+   or exceptions.  It can't be in errors.c because it can be
+   overridden (at link time) by a more powerful version implemented in
+   signalmodule.c. */
+
+#include "Python.h"
+
+/* ARGSUSED */
+int
+PyErr_CheckSignals(void)
+{
+	if (!PyOS_InterruptOccurred())
+		return 0;
+	PyErr_SetNone(PyExc_KeyboardInterrupt);
+	return -1;
+}