Write tests for new APE loader and fix bugs

- Add FreeBSD-specific mmap() flags
- Reduce size of the APE loader from 8kb to 4kb
- Work towards fixing the Makefile build on WSL
- Automate testing of APE no-modify-self behaviors
- Make the ape.S shell script code cleaner and tinier
- Improve the APE sanity check to test behavior better
- Fixed issue with ShowCrashReports() sigaltstack() on BSDs
- Delete symbols for S_MODE magnums which wasted compile time

If you checked out yesterday's APE commit, please run:

    rm -f /usr/bin/ape o/tmp/ape /tmp/ape "${TMPDIR:-/tmp}/ape"

Because this change fixes certain aspects of the new ABI. We don't have
automated migrations for APE loader versions yet. Thanks! You can also
download prebuilt binaries here:

- https://justine.lol/ape.elf    (Linux/FreeBSD/NetBSD/OpenBSD)
- https://justine.lol/ape.macho  (Apple)

Install the appropriate one as `/usr/bin/ape`.

libc/log/showcrashreports.c

@@ -106,8 +106,10 @@ void ShowCrashReports(void) {
     bzero(&ss, sizeof(ss));
     ss.ss_flags = 0;
     ss.ss_size = SIGSTKSZ;
+    // FreeBSD sigaltstack() will EFAULT if we use MAP_STACK here
+    // OpenBSD sigaltstack() auto-applies MAP_STACK to the memory
     if ((ss.ss_sp = mmap(0, GetStackSize(), PROT_READ | PROT_WRITE,
-                         MAP_STACK | MAP_ANONYMOUS, -1, 0))) {
+                         MAP_PRIVATE | MAP_ANONYMOUS, -1, 0))) {
       if (!sigaltstack(&ss, &g_oldsigaltstack)) {
         __cxa_atexit(FreeSigAltStack, ss.ss_sp, 0);
       } else {