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`.

ape/apeinstall.sh

@@ -9,19 +9,19 @@ fi
 if [ -f o/depend ]; then
   # mkdeps.com build was successfully run so assume we can build
   echo >&2
-  echo running: make -j8 o//ape/ape >&2
-  make -j8 o//ape/ape || exit
+  echo running: make -j8 o//ape/ape.elf >&2
+  make -j8 o//ape/ape.elf || exit
   echo done >&2
 else
   # no evidence we can build, use prebuilt one
   mkdir -p o//ape || exit
-  cp -af build/bootstrap/ape o//ape/ape
+  cp -af build/bootstrap/ape.elf o//ape/ape.elf
 fi
 
 echo >&2
-echo installing o//ape/ape to /usr/bin/ape >&2
-echo sudo mv -f o//ape/ape /usr/bin/ape >&2
-sudo mv -f o//ape/ape /usr/bin/ape || exit
+echo installing o//ape/ape.elf to /usr/bin/ape >&2
+echo sudo mv -f o//ape/ape.elf /usr/bin/ape >&2
+sudo mv -f o//ape/ape.elf /usr/bin/ape || exit
 echo done >&2
 
 if [ -e /proc/sys/fs/binfmt_misc/APE ]; then