Make configure test for tanh(-0.) == -0. committed in r62447 actually

work.  (The test wasn't properly linked with libm.  Sigh.)

configure

@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 62145 .
+# From configure.in Revision: 62447 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.61 for python 2.6.
 #
@@ -20852,6 +20852,9 @@ fi
 # * Check for mathematical functions *
 # ************************************
 
+LIBS_SAVE=$LIBS
+LIBS="$LIBS $LIBM"
+
 # On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of
 # -0. on some architectures.
 { echo "$as_me:$LINENO: checking whether tanh preserves the sign of zero" >&5
@@ -20871,6 +20874,7 @@ cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
 #include <math.h>
+#include <stdlib.h>
 int main() {
     /* return 0 if either negative zeros don't exist
        on this platform or if negative zeros exist
@@ -20927,8 +20931,6 @@ _ACEOF
 
 fi
 
-LIBS_SAVE=$LIBS
-LIBS="$LIBS $LIBM"
 
 for ac_func in hypot
 do

configure.in

@@ -2995,12 +2995,16 @@ fi],
 # * Check for mathematical functions *
 # ************************************
 
+LIBS_SAVE=$LIBS
+LIBS="$LIBS $LIBM"
+
 # On FreeBSD 6.2, it appears that tanh(-0.) returns 0. instead of
 # -0. on some architectures.
 AC_MSG_CHECKING(whether tanh preserves the sign of zero)
 AC_CACHE_VAL(ac_cv_tanh_preserves_zero_sign, [
 AC_TRY_RUN([
 #include <math.h>
+#include <stdlib.h>
 int main() {
     /* return 0 if either negative zeros don't exist
        on this platform or if negative zeros exist
@@ -3020,8 +3024,6 @@ then
   [Define if tanh(-0.) is -0., or if platform doesn't have signed zeros])
 fi
 
-LIBS_SAVE=$LIBS
-LIBS="$LIBS $LIBM"
 AC_REPLACE_FUNCS(hypot)
 
 AC_CHECK_FUNCS(acosh asinh atanh copysign expm1 finite isinf isnan log1p)