[scudo][standalone] Potential fix for missing sized delete

Summary:
In some setups, using `-fsized-deallocation` would end up not finding
a sized delete operator at link time. For now, avoid using the flag
and declare the sized delete operator in the cpp test only.

This is a tentative fix as I do not have the failing setup.

Reviewers: rnk, morehouse, hctim, eugenis, vitalybuka

Reviewed By: rnk, hctim

Subscribers: mgorny, delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D64086

llvm-svn: 365045