New stat structure.

* VFS and installed MFSes must be in sync before and after this change *

Use struct stat from NetBSD. It requires adding new STAT, FSTAT and LSTAT
syscalls. Libc modification is both backward and forward compatible.

Also new struct stat uses modern field sizes to avoid ABI
incompatibility, when we update uid_t, gid_t and company.
Exceptions are ino_t and off_t in old libc (though paddings added).

servers/rs/exec.c

@@ -12,7 +12,7 @@ static int exec_newmem(int proc_e, vir_bytes text_addr,
 	vir_bytes text_bytes, vir_bytes data_addr,
 	vir_bytes data_bytes, vir_bytes tot_bytes,
 	vir_bytes frame_len, int sep_id, int is_elf,
-	dev_t st_dev, ino_t st_ino, time_t st_ctime, char *progname,
+	dev_t st_dev, ino_t st_ino, time_t ctime, char *progname,
 	int new_uid, int new_gid, vir_bytes *stack_topp,
 	int *load_textp, int *allow_setuidp);
 static void patch_ptr(char stack[ARG_MAX], vir_bytes base);
@@ -321,7 +321,7 @@ static int exec_newmem(
   int is_elf,
   dev_t st_dev,
   ino_t st_ino,
-  time_t st_ctime,
+  time_t ctime,
   char *progname,
   int new_uid,
   int new_gid,
@@ -344,7 +344,7 @@ static int exec_newmem(
 	e.is_elf= is_elf;
 	e.st_dev= st_dev;
 	e.st_ino= st_ino;
-	e.st_ctime= st_ctime;
+	e.enst_ctime= ctime;
 	e.new_uid= new_uid;
 	e.new_gid= new_gid;
 	strncpy(e.progname, progname, sizeof(e.progname)-1);