We don't need to select a toolchain by the identifier when we get the proto from Starlark rules because in that case the proto contains a single toolchain.
The difference in toolchain_identifier field between the first and the second proto file will be caught as any other field.
RELNOTES: None.
PiperOrigin-RevId: 262543753
Change-Id: I1e66ee302bf551ade883c217f6269f44382393c0
While here, Also fix _read_crosstool_or_ctoolchain_proto to actually return the CToolchain found in the CROSSTOOL file, and add some missing \n.
RELNOTES: None.
PiperOrigin-RevId: 229926500