Put in defense against gcc -ffast-math.

configure

@@ -2442,6 +2442,7 @@ if test "$enable_debug" = yes && test "$ac_cv_prog_cc_g" = yes; then
 fi
 { echo "$as_me:$LINENO: using CFLAGS=$CFLAGS" >&5
 echo "$as_me: using CFLAGS=$CFLAGS" >&6;}
+
 # Check if the compiler still works with the template settings
 echo "$as_me:$LINENO: checking whether the C compiler still works" >&5
 echo $ECHO_N "checking whether the C compiler still works... $ECHO_C" >&6
@@ -2488,6 +2489,52 @@ echo "$as_me: error: cannot proceed" >&2;}
    { (exit 1); exit 1; }; }
 fi
 rm -f conftest.$ac_objext conftest$ac_exeext conftest.$ac_ext
+
+# Defend against gcc -ffastmath
+if test "$GCC" = yes; then
+cat >conftest.$ac_ext <<_ACEOF
+#line $LINENO "configure"
+#include "confdefs.h"
+
+#ifdef F77_DUMMY_MAIN
+#  ifdef __cplusplus
+     extern "C"
+#  endif
+   int F77_DUMMY_MAIN() { return 1; }
+#endif
+int
+main ()
+{
+#ifdef __FAST_MATH__
+choke me
+#endif
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
+  (eval $ac_compile) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+         { ac_try='test -s conftest.$ac_objext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  :
+else
+  echo "$as_me: failed program was:" >&5
+cat conftest.$ac_ext >&5
+{ { echo "$as_me:$LINENO: error: do not put -ffast-math in CFLAGS" >&5
+echo "$as_me: error: do not put -ffast-math in CFLAGS" >&2;}
+   { (exit 1); exit 1; }; }
+fi
+rm -f conftest.$ac_objext conftest.$ac_ext
+fi
+
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'