[Support] Remove llvm::is_trivially_{copy/move}_constructible

This restores D132311, which was reverted in
29c841ce (Sep 2022) due to certain files
not buildable with GCC 7.3.0. The previous attempt was reverted by
6cd9608f (Dec 2020).

This time, GCC 7.3.0 has existing build errors for a long time due to
structured bindings for many files, e.g.

```
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:9098:13: error: cannot decompose class type ‘std::pair<llvm::Value*, const llvm::SCEV*>’: both it and it
s base class ‘std::pair<llvm::Value*, const llvm::SCEV*>’ have non-static data members
   for (auto [_, Stride] : Legal->getLAI()->getSymbolicStrides()) {
             ^~~~~~~~~~~
```

... and also some `error: duplicate initialization of` instances due to llvm/Transforms/IPO/Attributor.h.

---

GCC 7.5.0 has a bug that, without this change, certain `SmallVector` with a `std::pair` element type like `SmallVector<std::pair<Instruction * const, Info>, 0> X;` lead to spurious

```
/tmp/opt/gcc-7.5.0/include/c++/7.5.0/type_traits:878:48: error: constructor required before non-static data member for ‘...’ has been parsed
```

Switching to std::is_trivially_{copy/move}_constructible fixes the error.