From:
http://buildroot.uclibc.org/cgi-bin/viewcvs.cgi/*checkout*/trunk/buildroot/toolchain/gcc/4.0.2/303-c99-complex-ugly-hack.patch?rev=11715

--- gcc-4.0.0/libstdc++-v3/configure-old	2005-04-30 22:04:48.061603912 -0500
+++ gcc-4.0.0/libstdc++-v3/configure	2005-04-30 22:06:13.678588152 -0500
@@ -7194,6 +7194,9 @@
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 #include <complex.h>
+#ifdef __UCLIBC__
+#error ugly hack to make sure configure test fails here for cross until uClibc supports the complex funcs
+#endif
 int
 main ()
 {