[llvm] [ADT] Fix implicit reliance on cassert in StringTable.h (PR #169324)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm can't see why not. It's not a great idea but it's not a reserved name or anything. In any case, relying on transitive includes is not ideal.

C++11 states: "A translation unit that includes a standard library header shall not #define or #undef names declared in
any standard library header."

https://github.com/llvm/llvm-project/pull/169324