check-armhf-time_t: make libsysprof-6-dev compile as C++

It uses the C99 restrict keyword, which C++ doesn't know, so #define it to nothing. With this change, the script reports:

[2024-02-24T11:11:58+00:00] => libsysprof-6-dev: base=>lfs, lfs=>time_t
[2024-02-24T11:11:59+00:00] <= libsysprof-6-dev: lfs=false, time_t=false

which I assume means there is no ABI problem.