[dsymutil] Prevent interleaved errors and warnings

[dsymutil] Prevent interleaved errors and warnings

Use a mutex to protect the printing of errors and warnings and prevents
interleaving. There are two sources of parallelism in dsymutil that
could result in interleaved output: errors from different architectures
being processed in parallel and errors from the analyze and clone steps
which execute in lockstep. This patch addresses both by using a unique
mutex across all error reporting.