Merge #20413: build: Require C++17 compiler

fac7198728 Use std::make_unique (MarcoFalke)
faaee810e6 build: Require C++17 compiler (MarcoFalke)

Pull request description:

  Developers have been compiling with C++17 for a few months now (fuzz tests and the msvc build have it even enabled by default). According to #16684, the 22.0 release shall be compiled with C++17 enabled.

  This only sets the build flag, any other changes need more discussion and can be done later.

ACKs for top commit:
  elichai:
    utACK fac7198728
  hebasto:
    ACK fac7198728, I've locally compiled on ARM 32bit SBC without GUI.
  fanquake:
    ACK fac7198728

Tree-SHA512: 53eb40ba5d496376a2d2cf16e2000bef36616cc2a3696c3ec59a5366e41fa8b872817a7ca21751f030f9c1efb339dfa63cc655eaa5199b9a3d2e52c2de0ccb29

src/util/memory.h

@@ -10,10 +10,11 @@
 #include <utility>
 
 //! Substitute for C++14 std::make_unique.
+//! DEPRECATED use std::make_unique in new code.
 template <typename T, typename... Args>
 std::unique_ptr<T> MakeUnique(Args&&... args)
 {
-    return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
+    return std::make_unique<T>(std::forward<Args>(args)...);
 }
 
 #endif