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/restoresigs.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/pylifecycle.h"
+/* clang-format off */
+
+/* Restore signals that the interpreter has called SIG_IGN on to SIG_DFL.
+ *
+ * All of the code in this function must only use async-signal-safe functions,
+ * listed at `man 7 signal` or
+ * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html.
+ */
+void
+_Py_RestoreSignals(void)
+{
+#ifdef SIGPIPE
+    PyOS_setsig(SIGPIPE, SIG_DFL);
+#endif
+#ifdef SIGXFZ
+    PyOS_setsig(SIGXFZ, SIG_DFL);
+#endif
+#ifdef SIGXFSZ
+    PyOS_setsig(SIGXFSZ, SIG_DFL);
+#endif
+}