Fix XNU / FreeBSD / OpenBSD / RHEL5 / NT bugs

For the first time ever, all tests in this codebase now pass, when
run automatically on macos, freebsd, openbsd, rhel5, rhel7, alpine
and windows via the network using the runit and runitd build tools

- Fix vfork exec path etc.
- Add XNU opendir() support
- Add OpenBSD opendir() support
- Add Linux history to syscalls.sh
- Use copy_file_range on FreeBSD 13+
- Fix system calls with 7+ arguments
- Fix Windows with greater than 16 FDs
- Fix RUNIT.COM and RUNITD.COM flakiness
- Fix OpenBSD munmap() when files are mapped
- Fix long double so it's actually long on Windows
- Fix OpenBSD truncate() and ftruncate() thunk typo
- Let Windows fcntl() be used on socket files descriptors
- Fix Windows fstat() which had an accidental printf statement
- Fix RHEL5 CLOCK_MONOTONIC by not aliasing to CLOCK_MONOTONIC_RAW

This is wonderful. I never could have dreamed it would be possible
to get it working so well on so many platforms with tiny binaries.

Fixes #31
Fixes #25
Fixes #14

libc/nexgen32e/environ.S

@@ -22,7 +22,8 @@
 /	Environment variable pointer list.
 	.bss
 	.align	8
-environ:.quad	0
+environ:
+	.quad	0
 	.endobj	environ,globl
 	.previous
 

libc/nexgen32e/memcpy.S

@@ -55,6 +55,7 @@ memcpy:	mov	%rdi,%rax
 /	@mode	long
 	.align	16
 MemCpy:	.leafprologue
+	.profilable
 	mov	$.Lmemcpytab.ro.size,%ecx
 	cmp	%rcx,%rdx
 	cmovb	%rdx,%rcx

libc/nexgen32e/memset.S

@@ -46,17 +46,15 @@ memset:	mov	%rdi,%rax
 /	@mode	long
 MemSet:	.leafprologue
 	.profilable
-	push	%rbx
-	movd	%esi,%xmm3
 	mov	$.Lmemsettab.ro.size,%ecx
 	cmp	%rcx,%rdx
 	cmovb	%rdx,%rcx
-	ezlea	memsettab,bx
-	jmp	*(%rbx,%rcx,8)
+	jmp	*memsettab(,%rcx,8)
 .Lanchorpoint:
 .L32r:	cmp	$1024,%rdx
 	jae	.Lerms
-.L32:	vpbroadcastb %xmm3,%ymm3
+.L32:	vmovd	%esi,%xmm3
+	vpbroadcastb %xmm3,%ymm3
 	mov	$32,%ecx
 1:	lea	32(%rcx),%rcx
 	vmovdqu	%ymm3,-64(%rdi,%rcx)
@@ -67,7 +65,8 @@ MemSet:	.leafprologue
 	jmp	.L0
 .L16r:	cmp	$1024,%rdx
 	jae	.Lerms
-.L16:	pbroadcastb %xmm3
+.L16:	movd	%esi,%xmm3
+	pbroadcastb %xmm3
 	mov	$16,%ecx
 1:	lea	16(%rcx),%rcx
 	movdqu	%xmm3,-32(%rdi,%rcx)
@@ -75,19 +74,16 @@ MemSet:	.leafprologue
 	ja	1b
 	movdqu	%xmm3,-16(%rdi,%rdx)
 	pxor	%xmm3,%xmm3
-.L0:	pop	%rbx
-	.leafepilogue
-.L8:	movzbq	%sil,%rbx
-	mov	$0x0101010101010101,%rcx
-	imul	%rcx,%rbx
-	mov	%rbx,(%rdi)
-	mov	%rbx,-8(%rdi,%rdx)
+.L0:	.leafepilogue
+.L8:	movzbl	%sil,%ecx
+	imul	.Lb8(%rip),%rcx
+	mov	%rcx,(%rdi)
+	mov	%rcx,-8(%rdi,%rdx)
 	jmp	.L0
-.L4:	movzbl	%sil,%ebx
-	mov	$0x01010101,%ecx
-	imul	%ecx,%ebx
-	mov	%ebx,(%rdi)
-	mov	%ebx,-4(%rdi,%rdx)
+.L4:	movzbl	%sil,%ecx
+	imul	$0x01010101,%ecx,%ecx
+	mov	%ecx,(%rdi)
+	mov	%ecx,-4(%rdi,%rdx)
 	jmp	.L0
 .L3:	mov	%sil,2(%rdi)
 .L2:	mov	%sil,1(%rdi)
@@ -103,6 +99,10 @@ MemSet:	.leafprologue
 	jmp	.L0
 	.endfn	MemSet,globl,hidden
 
+	.rodata.cst8
+.Lb8:	.quad	0x0101010101010101
+	.previous
+
 	.initro 300,_init_memset
 memsettab.ro:
 	.byte	.L0 - .Lanchorpoint

libc/nexgen32e/strcspn.S

@@ -19,15 +19,16 @@
 #include "libc/macros.h"
 
 /	Returns prefix length, consisting of chars not in reject.
-/	a.k.a. Return index of first byte that's in charset.
 /
 /	@param	rdi is string
 /	@param	rsi is reject nul-terminated character set
+/	@return	rax is index of first byte in charset
 /	@see	strspn(), strtok_r()
 /	@asyncsignalsafe
 strcspn:
 	push	%rbp
 	mov	%rsp,%rbp
+	.profilable
 	sub	$16,%rsp
 	push	%rdi
 	mov	%rsi,%rdi