linux-user: Emulate the Anonymous: keyword in /proc/self/smaps

Core dumps produced by gdb's gcore when connected to qemu's gdbstub
lack stack. The reason is that gdb includes only anonymous memory in
core dumps, which is distinguished by a non-0 Anonymous: value.

Consider the mappings with PAGE_ANON fully anonymous, and the mappings
without it fully non-anonymous.

Tested-by: Helge Deller <deller@gmx.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
[rth: Update for open_self_maps_* rewrite]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/syscall.c

@@ -8167,7 +8167,7 @@ static void open_self_maps_4(const struct open_self_maps_data *d,
                 "Private_Clean:         0 kB\n"
                 "Private_Dirty:         0 kB\n"
                 "Referenced:            0 kB\n"
-                "Anonymous:             0 kB\n"
+                "Anonymous:             %lu kB\n"
                 "LazyFree:              0 kB\n"
                 "AnonHugePages:         0 kB\n"
                 "ShmemPmdMapped:        0 kB\n"
@@ -8180,6 +8180,7 @@ static void open_self_maps_4(const struct open_self_maps_data *d,
                 "THPeligible:    0\n"
                 "VmFlags:%s%s%s%s%s%s%s%s\n",
                 size_kb, page_size_kb, page_size_kb,
+                (flags & PAGE_ANON ? size_kb : 0),
                 (flags & PAGE_READ) ? " rd" : "",
                 (flags & PAGE_WRITE_ORG) ? " wr" : "",
                 (flags & PAGE_EXEC) ? " ex" : "",