CodeGen/AsmPrinter.h: Fix \param in r207369. [-Wdocumentation]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207384 91177308-0d34-0410-b5e6-96231b3b80d8
Teach the pass manager's execution dump to print the current time before
each line. This is particularly nice for tracking which run of
a particular pass over a particular function was slow.

This also required making the TimeValue string much more useful. First,
there is a standard format for writing out a date and time. Let's use
that rather than strings that would have to be parsed. Second, actually
output the nanosecond resolution that timevalue claims to have.

This is proving useful working on PR19499, so I figured it would be
generally useful to commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207385 91177308-0d34-0410-b5e6-96231b3b80d8