[Driver][unittest] Unbreak ToolChainTest.cpp compilation with -Werror

D157275 broke some buildbots that run with -Werror:

	https://lab.llvm.org/buildbot#builders/36/builds/36604
	https://lab.llvm.org/buildbot#builders/57/builds/29201

Avoid this by using an overlong line rather than appeasing `clang-format`.

(cherry picked from commit 18252e6c)