Shorten and correct some function-header comments.

Make "verbose" output MUCH nicer. Now it tells you when you are linking a
bytecode file, or an archive, and whether it's because you called it by name,
or because you gave it a -l option, and it says "Trying" before it takes
action and prints a message in the past tense afterwards.

Make LinkFiles not skip the first file in Files.

Make LinkFiles warn you if it can't find a file and LLVM_LIB_SEARCH_PATH is
unset.

llvm-svn: 9747