Python: Fix wrapper build on MSVC not having __cplusplus for BitHacks

[EchterAgo]

The BitHacks.h header needs the __cplusplus define to determine whether to include <bit>. The MSVC compiler only defines this when it is passed the /Zc:__cplusplus flag. The main library was already setting this flag, but it not set when building the Python wrapper, causing compilation to fail because countr_zero and popcount are being used without <bit> being included.

Fixes #612

[axxel]

Thanks for looking into this and providing a fix. Before merging it though, I'd like to ask if you could test an alternative approach that I would consider a more general solution:

diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index a06cd6e3..b49d4150 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -22,6 +22,11 @@ if (WINRT)
         -DWINRT
     )
 endif()
+if (MSVC)
+    set (ZXING_CORE_DEFINES ${ZXING_CORE_DEFINES}
+        /Zc:__cplusplus
+    )
+else()
 
 set (ZXING_CORE_LOCAL_DEFINES
     $<$<BOOL:${BUILD_READERS}>:-DZXING_BUILD_READERS>
@@ -34,7 +39,6 @@ if (MSVC)
         -D_CRT_SECURE_NO_WARNINGS
         -D_CRT_NONSTDC_NO_WARNINGS
         -DNOMINMAX
-        /Zc:__cplusplus
     )
 else()
     set (ZXING_CORE_LOCAL_DEFINES ${ZXING_CORE_LOCAL_DEFINES}

If that also fixes your issue, I'd commit that instead as it would also make sure that other client code that ends up including BitHacks.h has this defined as needed.

[EchterAgo]

Updated, it builds on MSVC

[axxel]

Thanks.