Fix build errors in the performance tests with MinGW-w64.
Fix build errors in the performance tests with MinGW-w64.

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branch : v0-8

cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two