fix: work around buggy NAN in some MSVC versions

See igraph/igraph#2701

Author: szhorvat

src/hzeta.c

@@ -51,6 +51,18 @@
 #include "hzeta.h"
 #include "plfit_error.h"
 
+/* Work around bug in some Windows SDK / MSVC versions where NAN is not a
+ * constant expression, triggering an error in the definition of
+ * hsl_sf_hzeta_eulermaclaurin_series_coeffs[] and 
+ * hsl_sf_hzeta_eulermaclaurin_series_majorantratios[] below.
+ * We re-define NAN to the value it had in earlier MSVC versions.
+ * See https://github.com/igraph/igraph/issues/2701
+ */
+#ifdef _MSC_VER
+#undef NAN
+#define NAN (-(float)(((float)(1e+300 * 1e+300)) * 0.0F))
+#endif
+
 /* imported from gsl_machine.h */
 
 #define GSL_LOG_DBL_MIN (-7.0839641853226408e+02)