Sync libm with upstream.

Change-Id: I8ac8ee52122ee19a2e423c3211092023cb4896eb
diff --git a/libm/upstream-freebsd/lib/msun/src/s_tanhf.c b/libm/upstream-freebsd/lib/msun/src/s_tanhf.c
index 04f09c6..f537be4 100644
--- a/libm/upstream-freebsd/lib/msun/src/s_tanhf.c
+++ b/libm/upstream-freebsd/lib/msun/src/s_tanhf.c
@@ -19,7 +19,9 @@
 #include "math.h"
 #include "math_private.h"
 
-static const float one=1.0, two=2.0, tiny = 1.0e-30, huge = 1.0e30;
+static const volatile float tiny = 1.0e-30;
+static const float one=1.0, two=2.0, huge = 1.0e30;
+
 float
 tanhf(float x)
 {