libc: Add ftruncate64 and improve 64-bit parameter syscall handling.

This patch improves the handling of 64-bit parameters in syscalls on ARM.
The ARM EABI mandates that 64-bit quantities be passed in even/odd register
pairs, which requires special treatment.

This allows us to simplify our implementations of pread() and pwrite()
and remove the C stubs for pread64() and pwrite64().

Also add ftruncate64() to <unistd.h>

Change-Id: I407e2fd223ba0093dd2d0b04c6152fadfc9ce3ef

Bug 3107933
diff --git a/libc/include/sys/linux-unistd.h b/libc/include/sys/linux-unistd.h
index 4a61724..f706d00 100644
--- a/libc/include/sys/linux-unistd.h
+++ b/libc/include/sys/linux-unistd.h
@@ -52,8 +52,8 @@
 int              acct (const char*  filepath);
 ssize_t          read (int, void*, size_t);
 ssize_t          write (int, const void*, size_t);
-ssize_t          __pread64 (int, void *, size_t, off_t, off_t);
-ssize_t          __pwrite64 (int, void *, size_t, off_t, off_t);
+ssize_t          pread64 (int, void *, size_t, off64_t);
+ssize_t          pwrite64 (int, void *, size_t, off64_t);
 int              __open (const char*, int, mode_t);
 int              __openat (int, const char*, int, mode_t);
 int              close (int);
@@ -83,6 +83,7 @@
 int              dup2 (int, int);
 int              select (int, struct fd_set *, struct fd_set *, struct fd_set *, struct timeval *);
 int              ftruncate (int, off_t);
+int              ftruncate64 (int, off64_t);
 int              getdents (unsigned int, struct dirent *, unsigned int);
 int              fsync (int);
 int              fdatasync (int);