sinpi,cospi,tanpi: float.h needed for week reference

The patch fixes the omission of '#include <float.h>', which is needed for
the weak reference on systems with LDBL_MANT_DIG == DBL_MANT_DIG.

PR:	218514
MFC after:	1 week

lib/msun/src/s_cospi.c

@@ -60,6 +60,7 @@
  *    cospi(nan) = nan.  Raises the "invalid" floating-point exception.
  */
 
+#include <float.h>
 #include "math.h"
 #include "math_private.h"
 

lib/msun/src/s_sinpi.c

@@ -63,6 +63,7 @@
  *    sinpi(nan) = nan.  Raises the "invalid" floating-point exception.
  */
 
+#include <float.h>
 #include "math.h"
 #include "math_private.h"
 

lib/msun/src/s_tanpi.c

@@ -63,6 +63,7 @@
  *    tanpi(nan) = NaN.  Raises the "invalid" floating-point exception.
  */
 
+#include <float.h>
 #include "math.h"
 #include "math_private.h"