Sync libm with upstream FreeBSD.

Upstream SHA 78599c32efed3247d165302a1fbe8d9203e38974.

Test: treehugger
Change-Id: Ib103d211315e320df89a6f0bcb30cd8ba67dd603
diff --git a/libm/upstream-freebsd/lib/msun/src/e_pow.c b/libm/upstream-freebsd/lib/msun/src/e_pow.c
index b4f6a5a..52b2f5c 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_pow.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_pow.c
@@ -10,7 +10,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD: head/lib/msun/src/e_pow.c 342851 2019-01-07 17:35:09Z pfg $");
+__FBSDID("$FreeBSD$");
 
 /* __ieee754_pow(x,y) return x**y
  *