Enable compilation of QUIC for (P)NaCl.

1. Moved QUIC source files to the list of files that are compiled in
net_nacl target.
2. Fixed 2 minor issues in the code related to compatibility with NaCl.

BUG=448838

Review URL: https://codereview.chromium.org/1265283003

Cr-Commit-Position: refs/heads/master@{#341840}

net/base/iovec.h

@@ -5,14 +5,14 @@
 #ifndef NET_BASE_IOVEC_H_
 #define NET_BASE_IOVEC_H_
 
-#if defined(OS_POSIX)
+#if defined(OS_POSIX) && !defined(OS_NACL)
 #include <sys/uio.h>
 #else
 /* Structure for scatter/gather I/O.  */
 struct iovec {
   void* iov_base;  /* Pointer to data.  */
   size_t iov_len;  /* Length of data.  */
 };
-#endif  // defined(OS_LINUX)
+#endif  // defined(OS_POSIX) && !defined(OS_NACL)
 
 #endif  // NET_BASE_IOVEC_H_