lib: hack to make "float complex" works on newer GCC

I _like_ the "float complex" syntax and it's valid in C and I won't
go change all my C project to make it work with C++ ...

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

lib/iqbalance_optimize_c.cc

@@ -25,6 +25,17 @@
 #include <gr_io_signature.h>
 #include "iqbalance_optimize_c.h"
 
+#define GCC_VERSION (			\
+		__GNUC__ * 10000 +	\
+		__GNUC_MINOR__ * 100 +	\
+		__GNUC_PATCHLEVEL__	\
+	)
+
+#if GCC_VERSION >= 40800
+# define complex _Complex
+# undef _GLIBCXX_HAVE_COMPLEX_H
+#endif
+
 extern "C" {
 #include <osmocom/dsp/cxvec.h>
 #include <osmocom/dsp/iqbal.h>