Auto merge of #5391 - varkor:check-message, r=alexcrichton

Print "Checking" for cargo check

I often alternate between `check` and `build` and I'd like to be able to tell which is currently happening (short-term memory being what it is, and "compiling" implying to me that codegen is occurring). Changing the message to "Checking" seemed to be reasonable (and there was precedent for `doc` with "Documenting").

diff --cc tests/testsuite/cargotest/support/mod.rs
Simple merge