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

third_party/dlmalloc/dlmalloc.mk

@@ -58,7 +58,7 @@ o/$(MODE)/third_party/dlmalloc/dlmalloc.o:			\
 
 # we must segregate codegen because:
 #   file contains multiple independently linkable apis
-o/$(MODE)/third_party/dlmalloc/dlmalloc.greg.o:			\
+o/$(MODE)/third_party/dlmalloc/dlmalloc.o:			\
 		OVERRIDE_CFLAGS +=				\
 			-ffunction-sections			\
 			-fdata-sections

third_party/lua/lrepl.c

@@ -255,7 +255,7 @@ static ssize_t pushline (lua_State *L, int firstline) {
     rc = b ? 1 : -1;
   }
   if (!(rc == -1 && errno == EAGAIN)) {
-  write(1, "\n", 1);
+    write(1, "\n", 1);
   }
   if (rc == -1 || (!rc && !b)) {
     return rc;