arch-x86: build with getdents64 if system supports it

This patch makes it so the getdents64 syscall is built in gem5 if the
underlying host implements the syscall, similar to how the getdents
syscall is implemented.

The implementation for getdents64 already existed

Change-Id: I73b22c8df8df994f3f720e848a7d4f8cd31d318e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/46242
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Reviewed-by: Alex Dutu <alexandru.dutu@amd.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

src/arch/x86/linux/syscall_tbl32.cc

@@ -261,7 +261,11 @@ SyscallDescTable<EmuLinux::SyscallABI32> EmuLinux::syscallDescs32 = {
     { 218, "mincore" },
     { 219, "madvise", ignoreFunc },
     { 220, "madvise1" },
+#if defined(SYS_getdents64)
+    { 221, "getdents64", getdents64Func },
+#else
     { 221, "getdents64" },
+#endif
     { 222, "fcntl64" },
     { 223, "unused" },
     { 224, "gettid", gettidFunc },

src/arch/x86/linux/syscall_tbl64.cc

@@ -257,7 +257,11 @@ SyscallDescTable<EmuLinux::SyscallABI64> EmuLinux::syscallDescs64 = {
     { 214, "epoll_ctl_old" },
     { 215, "epoll_wait_old" },
     { 216, "remap_file_pages" },
+#if defined(SYS_getdents64)
+    { 217, "getdents64", getdents64Func },
+#else
     { 217, "getdents64" },
+#endif
     { 218, "set_tid_address", setTidAddressFunc },
     { 219, "restart_syscall" },
     { 220, "semtimedop" },