Fix C++11 build failure in destroy_at

[kiranj26]

Summary

This fixes a C++11 compatibility issue in src/Defines.h.

In the C++11 code path, destroy_at was declared as:

• constexpr void destroy_at(T* p)

With Apple Clang (C++11), this fails to compile because constexpr functions in C++11 cannot have void return type.

This change updates the C++11 overload to:

• inline void destroy_at(T* p)

C++14 and C++17+ paths are unchanged.

Why this change

build_test.sh fails on C++11 toolchains due to the constexpr void declaration, which blocks normal development and CI on affected compilers.

Validation

• Ran ./build_test.sh successfully after the change.
• Ran ./build/test/test_EmbeddedProto successfully (155 tests passed).

Scope

• Single-file, minimal change:
  • src/Defines.h

Issue

Closes #89