Fix the -lm configure test; fixes #4155

configure.ac

@@ -780,8 +780,11 @@ dnl    Keep that check as early as possible.
 dnl    as we need to know whether we need libm
 dnl    for math functions or not
 dnl    (see http://hackage.haskell.org/trac/ghc/ticket/3730)
-AC_SEARCH_LIBS(atan, m, 
-  [AC_DEFINE([HAVE_LIBM], [1], [Define to 1 if you need to link with libm])])
+AC_CHECK_LIB(m, atan, HaveLibM=YES, HaveLibM=NO)
+if test $HaveLibM = YES
+then
+  AC_DEFINE([HAVE_LIBM], [1], [Define to 1 if you need to link with libm])
+fi
 
 dnl ** check whether this machine has BFD and liberty installed (used for debugging)
 dnl    the order of these tests matters: bfd needs liberty