syscall: force O_LARGEFILE in Linux open system call

Fixes #717.

R=adg, PeterGo
CC=golang-dev
https://golang.org/cl/1032041
diff --git a/src/pkg/syscall/zsyscall_linux_amd64.go b/src/pkg/syscall/zsyscall_linux_amd64.go
index 030bed2..c5daf0d 100644
--- a/src/pkg/syscall/zsyscall_linux_amd64.go
+++ b/src/pkg/syscall/zsyscall_linux_amd64.go
@@ -5,6 +5,13 @@
 
 import "unsafe"
 
+func open(path string, mode int, perm int) (fd int, errno int) {
+	r0, _, e1 := Syscall(SYS_OPEN, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(mode), uintptr(perm))
+	fd = int(r0)
+	errno = int(e1)
+	return
+}
+
 func pipe(p *[2]_C_int) (errno int) {
 	_, _, e1 := Syscall(SYS_PIPE, uintptr(unsafe.Pointer(p)), 0, 0)
 	errno = int(e1)
@@ -314,13 +321,6 @@
 	return
 }
 
-func Open(path string, mode int, perm int) (fd int, errno int) {
-	r0, _, e1 := Syscall(SYS_OPEN, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(mode), uintptr(perm))
-	fd = int(r0)
-	errno = int(e1)
-	return
-}
-
 func Openat(dirfd int, path string, flags int, mode int) (fd int, errno int) {
 	r0, _, e1 := Syscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(flags), uintptr(mode), 0, 0)
 	fd = int(r0)