Add automatic TMPDIR setup/teardown to GNU Make

We now guarantee TMPDIR will be defined on a per build rule basis. It'll
be an absolute path. It'll be secure and unique. It'll be rm -rf'd after
the last shell script line in your build rule is executed. If $TMPDIR is
already defined, then it'll be created as a subdirectory of your $TMPDIR
and then replace the variable with the new definition. The Landlock Make
repository will be updated with examples shortly after this change which
shall be known as Landlock Make 1.1.1.

See #530

libc/tinymath/fmod-tiny.S

@@ -0,0 +1,33 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/macros.internal.h"
+#ifdef TINY
+
+//	fmod [sic] does (𝑥 rem 𝑦) w/ round()-style rounding.
+//
+//	@param	𝑥 is double passed in lower half of %xmm0
+//	@param	𝑦 is double passed in lower half of %xmm1
+//	@return	remainder ∈ (-|𝑦|,|𝑦|) in %xmm0
+//	@define	𝑥-trunc(𝑥/𝑦)*𝑦
+//	@see	emod()
+fmod:	ezlea	fmodl,ax
+	jmp	_d2ld2
+	.endfn	fmod,globl
+
+#endif /* TINY */