Edit OpenCVFindLAPACK.cmake

Change:

if(NOT " ${__content_str}" STREQUAL " ${_lapack_include_str}")
  file(WRITE "${CBLAS_H_PROXY_PATH}" "${_lapack_include_str}")
endif()

To:

if(NOT " ${__content_str}" STREQUAL " ${_lapack_include_str}")
  file(WRITE "${CBLAS_H_PROXY_PATH}" "extern 'C' { ${_lapack_include_str} }")
endif()