Add a missing extern in specfunc_wrappers.c

--- a/scipy/special/specfun_wrappers.c
+++ b/scipy/special/specfun_wrappers.c
@@ -35,6 +35,7 @@
 extern void F_FUNC(itairy,ITAIRY)(double*,double*,double*,double*,double*);
 extern void F_FUNC(e1xb,E1XB)(double*,double*);
 extern void F_FUNC(e1z,E1Z)(npy_cdouble*,npy_cdouble*);
+extern void F_FUNC(eixz,EIXZ)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(eix,EIX)(double*,double*);
 extern void F_FUNC(cerror,CERROR)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(stvh0,STVH0)(double*,double*);