Make fixes and improvements

- Document more compiler flags
- Expose new __print_maps() api
- Better overflow checking in mmap()
- Improve the shell example somewhat
- Fix minor runtime bugs regarding stacks
- Make kill() on fork()+execve()'d children work
- Support CLONE_CHILD_CLEARTID for proper joining
- Fix recent possible deadlock regression with --ftrace

libc/nt/kernel32/CreateToolhelp32Snapshot.s

@@ -1,2 +1,12 @@
 .include "o/libc/nt/codegen.inc"
-.imp	kernel32,__imp_CreateToolhelp32Snapshot,CreateToolhelp32Snapshot,250
+.imp	kernel32,__imp_CreateToolhelp32Snapshot,CreateToolhelp32Snapshot,0
+
+	.text.windows
+CreateToolhelp32Snapshot:
+	push	%rbp
+	mov	%rsp,%rbp
+	.profilable
+	mov	__imp_CreateToolhelp32Snapshot(%rip),%rax
+	jmp	__sysv2nt
+	.endfn	CreateToolhelp32Snapshot,globl
+	.previous

libc/nt/kernel32/Process32FirstW.s

@@ -1,2 +1,12 @@
 .include "o/libc/nt/codegen.inc"
-.imp	kernel32,__imp_Process32FirstW,Process32FirstW,1065
+.imp	kernel32,__imp_Process32FirstW,Process32FirstW,0
+
+	.text.windows
+Process32First:
+	push	%rbp
+	mov	%rsp,%rbp
+	.profilable
+	mov	__imp_Process32FirstW(%rip),%rax
+	jmp	__sysv2nt
+	.endfn	Process32First,globl
+	.previous

libc/nt/kernel32/Process32NextW.s

@@ -1,2 +1,12 @@
 .include "o/libc/nt/codegen.inc"
-.imp	kernel32,__imp_Process32NextW,Process32NextW,1067
+.imp	kernel32,__imp_Process32NextW,Process32NextW,0
+
+	.text.windows
+Process32Next:
+	push	%rbp
+	mov	%rsp,%rbp
+	.profilable
+	mov	__imp_Process32NextW(%rip),%rax
+	jmp	__sysv2nt
+	.endfn	Process32Next,globl
+	.previous