[ThinLTO] Debug message cleanup (NFC)

Added some missing spaces between the module identifier and the start of
the debug message. Also added a ":" after the module identifier to make
this look a little nicer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255259 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed