Begin incorporating Python unit tests into build

We now build a separate APE binary for each test so they can run in
parallel. We've got 148 tests running fast and stable so far.

third_party/python/Python/initsigs.c

@@ -0,0 +1,30 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=4 sts=4 sw=4 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Python 3                                                                     │
+│ https://docs.python.org/3/license.html                                       │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/sysv/consts/sig.h"
+#include "third_party/python/Include/intrcheck.h"
+#include "third_party/python/Include/pyerrors.h"
+#include "third_party/python/Include/pylifecycle.h"
+/* clang-format off */
+
+void
+_Py_InitSigs(void)
+{
+#ifdef SIGPIPE
+    PyOS_setsig(SIGPIPE, SIG_IGN);
+#endif
+#ifdef SIGXFZ
+    PyOS_setsig(SIGXFZ, SIG_IGN);
+#endif
+#ifdef SIGXFSZ
+    PyOS_setsig(SIGXFSZ, SIG_IGN);
+#endif
+    PyOS_InitInterrupts(); /* May imply initsignal() */
+    if (PyErr_Occurred()) {
+        Py_FatalError("Py_Initialize: can't import signal");
+    }
+}