Update to FreeBSD libm r336523.

This includes an ld128 powl, plus the clog* and cpow* families.

Also teach the NOTICE generator to strip SPDX-License-Identifier lines.

Bug: N/A
Test: ran tests
Change-Id: Ic8289d1253666a19468a4088884cf7540f1ec66d
diff --git a/libm/upstream-freebsd/lib/msun/bsdsrc/b_tgamma.c b/libm/upstream-freebsd/lib/msun/bsdsrc/b_tgamma.c
index 1d0af44..e530649 100644
--- a/libm/upstream-freebsd/lib/msun/bsdsrc/b_tgamma.c
+++ b/libm/upstream-freebsd/lib/msun/bsdsrc/b_tgamma.c
@@ -1,4 +1,6 @@
 /*-
+ * SPDX-License-Identifier: BSD-4-Clause
+ *
  * Copyright (c) 1992, 1993
  *	The Regents of the University of California.  All rights reserved.
  *
@@ -33,7 +35,7 @@
 
 /* @(#)gamma.c	8.1 (Berkeley) 6/4/93 */
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
+__FBSDID("$FreeBSD: head/lib/msun/bsdsrc/b_tgamma.c 325966 2017-11-18 14:26:50Z pfg $");
 
 /*
  * This code by P. McIlroy, Oct 1992;