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/mem/memalign.S

@@ -18,22 +18,18 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/macros.internal.h"
 #include "libc/notice.inc"
-.source	__FILE__
 
 //	Allocates aligned memory.
 //
 //	Returns a pointer to a newly allocated chunk of n bytes, aligned in
-//	accord with the alignment argument. The alignment argument should be
-//	a power of two. If the argument is not a power of two, the nearest
-//	greater power is used. 8-byte alignment is guaranteed by normal
-//	malloc calls, so don't bother calling memalign with an argument of 8
-//	or less.
+//	accord with the alignment argument. The alignment argument shall be
+//	rounded up to the nearest two power and higher 2 powers may be used
+//	if the allocator imposes a minimum alignment requirement.
 //
-//	@param	rdi is alignment in bytes
-//	@param	rsi (newsize) is number of bytes needed
+//	@param	rdi is alignment in bytes, coerced to 1+ w/ 2-power roundup
+//	@param	rsi is number of bytes needed, coerced to 1+
 //	@return	rax is memory address, or NULL w/ errno
-//	@note	overreliance on memalign is a sure way to fragment space
-//	@see	dlmemalign()
+//	@see	valloc(), pvalloc()
 memalign:
 	jmp	*hook_memalign(%rip)
 	.endfn	memalign,globl