Improve memory safety

This commit makes numerous refinements to cosmopolitan memory handling.

The default stack size has been reduced from 2mb to 128kb. A new macro
is now provided so you can easily reconfigure the stack size to be any
value you want. Work around the breaking change by adding to your main:

    STATIC_STACK_SIZE(0x00200000);  // 2mb stack

If you're not sure how much stack you need, then you can use:

    STATIC_YOINK("stack_usage_logging");

After which you can `sort -nr o/$MODE/stack.log`. Based on the unit test
suite, nothing in the Cosmopolitan repository (except for Python) needs
a stack size greater than 30kb. There are also new macros for detecting
the size and address of the stack at runtime, e.g. GetStackAddr(). We
also now support sigaltstack() so if you want to see nice looking crash
reports whenever a stack overflow happens, you can put this in main():

    ShowCrashReports();

Under `make MODE=dbg` and `make MODE=asan` the unit testing framework
will now automatically print backtraces of memory allocations when
things like memory leaks happen. Bugs are now fixed in ASAN global
variable overrun detection. The memtrack and asan runtimes also handle
edge cases now. The new tools helped to identify a few memory leaks,
which are fixed by this change.

This change should fix an issue reported in #288 with ARG_MAX limits.
Fixing this doubled the performance of MKDEPS.COM and AR.COM yet again.

libc/sysv/systemfive.S

@@ -21,6 +21,7 @@
 #include "libc/sysv/consts/nr.h"
 #include "libc/sysv/consts/map.h"
 #include "libc/macros.internal.h"
+#include "libc/sysv/consts/prot.h"
 #include "libc/nexgen32e/macros.h"
 
 /*                                           ▄▄▄
@@ -349,6 +350,34 @@ _init_systemfive_stack:					# determinism ftw!
 	syscall
 2:	test	%rax,%rax
 	js	1b
+
+//	prevent operating system from auto-mapping stack
+//	we guarantee stack overflows are always detected
+//	so long as you never use -DSTACK_FRAME_UNLIMITED
+//	TODO: Why does this fail sometimes with FreeBSD?
+	testb	IsFreebsd()
+	jnz	9f
+	push	%rax
+	push	%rdx
+	push	%r11
+	mov	__NR_mprotect,%eax
+	mov	$PAGESIZE,%esi
+	xor	%edx,%edx				# PROT_NONE
+	syscall
+	pop	%r11
+	pop	%rdx
+	pop	%rax
+9:	
+
+//	update the memory intervals
+//	m.i		0	4
+//	m.n		8	4
+//	m.p		16	8
+//	m.p[0].x	24	4
+//	m.p[0].y	28	4
+//	m.p[0].h	32	8
+//	m.p[0].prot	40	4
+//	m.p[0].flags	44	4
 	.weak	_mmi
 	ezlea	_mmi,cx
 	test	%rcx,%rcx
@@ -360,12 +389,14 @@ _init_systemfive_stack:					# determinism ftw!
 	movb	$1,(%rcx)				# _mmi.i
 	mov	%r11d,24(%rcx)				# _mmi.s[0].x
 	mov	%r9d,28(%rcx)				# _mmi.s[0].y
-	mov	%edx,36(%rcx)				# _mmi.s[0].prot
-	mov	%r10d,40(%rcx)				# _mmi.s[0].flags
+	orq	$-1,32(%rcx)				# _mmi.s[0].h
+	mov	%edx,40(%rcx)				# _mmi.s[0].prot
+	mov	%r10d,44(%rcx)				# _mmi.s[0].flags
 3:	pop	%r9					# restore stack size
 	pop	%rsi
 	pop	%rdi
 	leave
+//	switch stacks
 	pop	%rcx
 	lea	(%rax,%r9),%rsp
 	sub	$ape_stack_align,%rsp			# openbsd:stackbound