[IRGen] Conditionalise use of sized deallocation.

[al45tair]

Sized deallocation isn't enabled everywhere, so we need to check for it before using it.

[al45tair]

@swift-ci Please smoke test

[al45tair]

This should fix build errors I'm seeing, e.g.

/.../swift-project/swift/lib/IRGen/ProtocolInfo.h:237:5: error: no matching function for call to 'operator delete'
  237 |     ::operator delete(ptr, size);
      |     ^~~~~~~~~~~~~~~~~

after #83321 landed.

[compnerd]

Hmm, I wonder if we should be avoiding the use of the sized allocation similarly.

edit
C++11 treated the two parameter as a placement deletion. C++14 changed that to the sized deletion by default. Clang is the odd compiler that requires -fsized-deallocation flag, MSVC and GCC should enable that by default on C++14 and newer.

[al45tair]

Hmm, I wonder if we should be avoiding the use of the sized allocation similarly.

I'm not sure what you mean — operator new always takes a size, doesn't it?

[al45tair]

(The changes in this PR fixed my local build.)

[compnerd]

The issue here was identified by ASAN - we are mismatching the new/delete operation (doing partial frees). I think that this is safe to apply, but I'm wondering if we should be doing something else for the memory handling. Perhaps we should look into bump allocators for the type information rather than using operator new.

[al45tair]

Closed in favour of #83399