* Set -Wno-deprecated-declarations for Intel

Intel compiler silently ignores -Wno-deprecated-declarations
so warning no. 1786 must be explicitly suppressed.

* Make std::int64_t → double casts explicit

While std::int64_t → double is a perfectly conformant
implicit conversion, Intel compiler warns about it.
Make them explicit via static_cast<double>.

* Make std::int64_t → int casts explicit

Intel compiler warns about emplacing an std::int64_t
into an int container. Just make the conversion explicit
via static_cast<int>.

* Cleanup Intel -Wno-deprecated-declarations workaround logic