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/intrin/intrin.mk

@@ -58,11 +58,21 @@ o/$(MODE)/libc/intrin/asan.o:				\
 			-finline			\
 			-finline-functions
 
+# we can't use compiler magic because:
+#   kprintf() is mission critical to error reporting
+o/$(MODE)/libc/intrin/getmagnumstr.greg.o		\
+o/$(MODE)/libc/intrin/strerrno.greg.o			\
+o/$(MODE)/libc/intrin/strerrdoc.greg.o			\
+o/$(MODE)/libc/intrin/strerror_wr.greg.o		\
 o/$(MODE)/libc/intrin/kprintf.greg.o:			\
 		OVERRIDE_CFLAGS +=			\
 			-fpie				\
+			-fwrapv				\
+			-x-no-pg			\
+			-mno-fentry			\
 			-ffreestanding			\
-			$(NO_MAGIC)
+			-fno-sanitize=all		\
+			-fno-stack-protector
 
 o/$(MODE)/libc/intrin/tls.greg.o			\
 o/$(MODE)/libc/intrin/exit.greg.o			\