[clang][driver] Fix null pointer dereference warning inside PrintActions1 (PR43462)

As detailed on PR43462, clang static analyzer is complaining about a null pointer dereference as we provide a 'host' toolchain fallback if the ToolChain pointer is null, but then use that pointer anyhow to report the triple.

Tests indicate the ToolChain pointer is always valid and the 'host' code path is redundant.

Differential Revision: https://reviews.llvm.org/D74046