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.h

@@ -1,14 +1,13 @@
 #ifndef COSMOPOLITAN_APE_LOADER_H_
 #define COSMOPOLITAN_APE_LOADER_H_
 
-#define APE_LOADER_BASE    0x200000
-#define APE_LOADER_SIZE    0x200000
-#define APE_LOADER_BSS     (PAGESIZE * 2)
-#define APE_LOADER_STACK   0x7f0000000000
-#define APE_LOADER_ENTRY   (APE_LOADER_BASE + 0x47)
-#define APE_LOADER_SYSCALL (APE_LOADER_BASE + 0x50)
-#define APE_BLOCK_BASE     0x7e0000000000
-#define APE_BLOCK_SIZE     0x000200000000
+#define APE_LOADER_BASE  0x200000
+#define APE_LOADER_SIZE  0x200000
+#define APE_LOADER_ENTRY 0x200400
+#define APE_LOADER_BSS   (PAGESIZE * 2)
+#define APE_LOADER_STACK 0x7f0000000000
+#define APE_BLOCK_BASE   0x7e0000000000
+#define APE_BLOCK_SIZE   0x000200000000
 
 struct ApeLoader {
   int fd;