The upstream commit: https://reviews.llvm.org/D151590
added a new flag to mark target specific compiler options.
The side effect of it was that in cases when -### or -v is used without any
input file, clang started emitting an error.
It happened like that becasue there is no compilation actions created
which could consume/verify these target specific options.
This patch changes that error to a warning about unused option, in situations
when there is no actions and still generates error when there are actions.