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/runtime/runtime.h

@@ -112,6 +112,7 @@ void __morph_begin(void);
 void __morph_end(void);
 unsigned char *GetFirstInstruction(void);
 unsigned char *GetInstructionLengths(void);
+void __print_maps(void);
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */