Fix implicit __isinf declarations in exp.

My recent exp patch introduced warnings about implicit __isinf
declarations in exp because e_exp.c didn't include <math.h>.  This
patch fixes this.  Because <math.h> can't be included after
<math_private.h> (because of macro definitions of __nan*), it was
necessary to put an include in sysdeps/x86_64/fpu/multiarch/e_exp.c as
well.

Tested x86_64.

	* sysdeps/ieee754/dbl-64/e_exp.c: Include <math.h>.
	* sysdeps/x86_64/fpu/multiarch/e_exp.c
	[HAVE_FMA4_SUPPORT || HAVE_AVX_SUPPORT]: Likewise.

ChangeLog

@@ -1,3 +1,9 @@
+2014-03-24  Joseph Myers  <joseph@codesourcery.com>
+
+	* sysdeps/ieee754/dbl-64/e_exp.c: Include <math.h>.
+	* sysdeps/x86_64/fpu/multiarch/e_exp.c
+	[HAVE_FMA4_SUPPORT || HAVE_AVX_SUPPORT]: Likewise.
+
 2014-03-24  Paul Pluzhnikov  <ppluzhnikov@google.com>
 
 	[BZ #16634]

sysdeps/ieee754/dbl-64/e_exp.c

@@ -32,6 +32,7 @@
 /*                                                                         */
 /***************************************************************************/
 
+#include <math.h>
 #include "endian.h"
 #include "uexp.h"
 #include "mydefs.h"

sysdeps/x86_64/fpu/multiarch/e_exp.c

@@ -1,5 +1,6 @@
 #if defined HAVE_FMA4_SUPPORT || defined HAVE_AVX_SUPPORT
 # include <init-arch.h>
+# include <math.h>
 # include <math_private.h>
 
 extern double __ieee754_exp_sse2 (double);