add QT_LIBINFIX property support

[Elite-stay]

mkspecs/qconfig.pri QT_LIBINFIX

[waruqi]

都测试验证过么，5.x , 6.x 官方 sdk ，最好都测下，避免 break

[Issues-translate-bot]

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Have they been tested and verified? 5.x, 6.x official sdk, it is best to test them all to avoid break

[Elite-stay]

都测试验证过么，5.x , 6.x 官方 sdk ，最好都测下，避免 break

测的5.4.1的，6.x的我晚上再试一下吧

[Issues-translate-bot]

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Have they been tested and verified? 5.x, 6.x official sdk, it is best to test them all to avoid break

I tested 5.4.1 and 6.x. I’ll try it again tonight.

[Elite-stay]

都测试验证过么，5.x , 6.x 官方 sdk ，最好都测下，避免 break

6.x 测试也通过了

[Issues-translate-bot]

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Have they been tested and verified? 5.x, 6.x official sdk, it is best to test them all to avoid break

6.x test also passed