configure.ac: remove extra -lm check, move dl check to after libm check

In addition, do not fail the configure if libdl[d] is not found.
Building may still fail in that case, but then it may not :)

cde/configure.ac

@@ -431,6 +431,8 @@ AC_CHECK_HEADERS([X11/extensions/Xrender.h], [],
 
 dnl libraries
 AC_CHECK_LIB(m, cosf)
+AC_SEARCH_LIBS(dlopen, [dl dld], [], [])
+
 AC_CHECK_LIB(crypt, crypt)
 dnl this should be configurable, for now it is required
 AC_CHECK_LIB(Xinerama, XineramaQueryScreens,
@@ -506,13 +508,6 @@ AC_CHECK_LIB(Xdmcp, XdmcpFlush, [XDMCPLIB="-lXdmcp"], [XDMCPLIB=""],
                  [${EXTRA_INCS} ${EXTRA_LIBS}])
 AC_SUBST(XDMCPLIB)
 
-AC_SEARCH_LIBS(cos, m, [], [
-	AC_MSG_ERROR([cos not found, your system probably doesn't obey posix])])
-
-AC_SEARCH_LIBS(dlopen, [dl dld], [], [
-	AC_MSG_ERROR([dlopen not found, your system probably doesn't obey posix]
-	)])
-
 dnl iconv
 AM_ICONV