sim-se: Add additional TGT_AT_* constants for Linux.

These constants are used by at least the newfstatat system call.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-1117

Change-Id: I1732f064aa7ef22995db7011a06112875b3f4c9b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53204
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/kern/linux/linux.hh

@@ -297,6 +297,9 @@ class Linux : public OperatingSystem
     // for *at syscalls
     static const int TGT_AT_FDCWD     = -100;
     static const int TGT_AT_REMOVEDIR = 0x200;
+    static const int TGT_AT_SYMLINK_FOLLOW = 0x400;
+    static const int TGT_AT_NO_AUTOMOUNT = 0x800;
+    static const int TGT_AT_EMPTY_PATH = 0x1000;
 
     // for MREMAP
     static const unsigned TGT_MREMAP_MAYMOVE    = 0x1;