Avoid removing macro _CRT_USE_C_COMPLEX_H if pre-existing (#393)

CHANGES

@@ -3,6 +3,7 @@ arpack-ng - 3.9.0
 [ Fabien Péan ]
 * CI: Enable job `windows_latest_cmake` to run all tests
 * CMake: Fix BLAS and LAPACK static library order needed to consume the library on Windows with static linkage
+* Fix using ARPACK on Windows with MSVC compiler from C++17 onwards
 
 [ Zhentao Wang ]
 * [BUG FIX] parpack.h and parpack.hpp: type of rwork should be real instead of complex.

arpackdef.h.in

@@ -14,9 +14,13 @@
 #define a_uint unsigned int
 #endif
 #ifdef _MSC_VER
+#ifndef _CRT_USE_C_COMPLEX_H
 #define _CRT_USE_C_COMPLEX_H
 #include <complex.h>
 #undef _CRT_USE_C_COMPLEX_H
+#else
+#include <complex.h>
+#endif
 #define a_fcomplex _Fcomplex
 #define a_dcomplex _Dcomplex
 #ifndef CMPLXF