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/loader.lds

@@ -17,16 +17,16 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 ENTRY(_start)
-OUTPUT_FORMAT(binary)
 
 SECTIONS {
   . = 0x200000;
   .text : {
     *(.text)
     *(.rodata .rodata.*)
-    . = ALIGN(4096);
+    . = ALIGN(64);
   }
   filesz = . - ehdr;
+  textsz = . - _start;
   .bss ALIGN(4096) : {
     bss = .;
     *(.bss)
@@ -39,3 +39,4 @@ SECTIONS {
 }
 
 bsssize = SIZEOF(.bss);
+textoff = _start - ehdr;