fixed redefinition error on clang 7.0.1 with musl

[sergiud]

Currently, it is not possible compile OpenCV 4.5.4 using Clang 7.0.1 + musl due to __WORDSIZE not being defined. As a consequence, the following error is issued:

opencv_contrib/modules/wechat_qrcode/src/zxing/common/bitarray.cpp:18:5: warning: '__WORDSIZE' is not defined, evaluates to 0 [-Wundef]
#if __WORDSIZE == 64
    ^
opencv_contrib/modules/wechat_qrcode/src/zxing/common/bitarray.cpp:21:23: error: typedef redefinition with different types ('long long' vs 'long')
typedef long long int int64_t;
                      ^
<...>/sysroots/core2-64-<snip>-linux-musl/usr/include/bits/alltypes.h:152:25: note: previous definition is here
typedef signed _Int64   int64_t;
                        ^
1 warning and 1 error generated.

Since the int64_t typedef is unused in the translation unit anyway, we can simply remove the definition.

Pull Request Readiness Checklist

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

build_image:Custom=ubuntu32:16.04
buildworker:Custom=linux-4,linux-6

[alalek]

Thank you 👍