Hide statfs/fstatfs' ST_VALID flag from userspace.

Spotted while debugging the strace 4.10 upgrade.

Change-Id: I1af1be9c9440151f55f74a835e1df71529b0e4fe
diff --git a/libc/arch-x86_64/syscalls/fstatfs64.S b/libc/arch-x86_64/syscalls/__fstatfs.S
similarity index 75%
rename from libc/arch-x86_64/syscalls/fstatfs64.S
rename to libc/arch-x86_64/syscalls/__fstatfs.S
index f727350..b50e355 100644
--- a/libc/arch-x86_64/syscalls/fstatfs64.S
+++ b/libc/arch-x86_64/syscalls/__fstatfs.S
@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(fstatfs64)
+ENTRY(__fstatfs)
     movl    $__NR_fstatfs, %eax
     syscall
     cmpq    $-MAX_ERRNO, %rax
@@ -12,7 +12,5 @@
     call    __set_errno_internal
 1:
     ret
-END(fstatfs64)
-
-    .globl fstatfs
-    .equ fstatfs, fstatfs64
+END(__fstatfs)
+.hidden __fstatfs
diff --git a/libc/arch-x86_64/syscalls/statfs64.S b/libc/arch-x86_64/syscalls/__statfs.S
similarity index 77%
rename from libc/arch-x86_64/syscalls/statfs64.S
rename to libc/arch-x86_64/syscalls/__statfs.S
index 16f6bdd..607a809 100644
--- a/libc/arch-x86_64/syscalls/statfs64.S
+++ b/libc/arch-x86_64/syscalls/__statfs.S
@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(statfs64)
+ENTRY(__statfs)
     movl    $__NR_statfs, %eax
     syscall
     cmpq    $-MAX_ERRNO, %rax
@@ -12,7 +12,5 @@
     call    __set_errno_internal
 1:
     ret
-END(statfs64)
-
-    .globl statfs
-    .equ statfs, statfs64
+END(__statfs)
+.hidden __statfs