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-macho.S

@@ -41,7 +41,7 @@ macho:	.long	0xFEEDFACE+1
 	.long	30f-20b
 	.ascin	"__TEXT",16
 	.quad	macho				# vaddr
-	.quad	filesz				# memsz
+	.quad	4096				# memsz
 	.quad	0				# file offset
 	.quad	filesz				# file size
 	.long	PROT_EXEC|PROT_READ|PROT_WRITE	# maxprot
@@ -53,7 +53,7 @@ macho:	.long	0xFEEDFACE+1
 	.quad	_start				# vaddr
 	.quad	textsz				# memsz
 	.long	textoff				# offset
-	.long	3				# align 2**3 = 8
+	.long	6				# align 2**3 = 64
 	.long	0				# reloc table offset
 	.long	0				# relocation count
 	.long	MAC_S_ATTR_SOME_INSTRUCTIONS	# section type & attributes
@@ -112,7 +112,7 @@ macho:	.long	0xFEEDFACE+1
 60:
 	.endobj	macho,globl
 
-	.align	8
+	.align	64
 _start:	mov	%rsp,%rsi
 	jmp	ApeLoader
 	.endfn	_start,globl