output directory for -fvtv-debug and -fvtv-counts

[Sandra Loosemore]

I noticed that the documentation for the -fvtv-* options in invoke.texi 
needed a little copy-editing and markup correction.  I started working 
on a patch, but I'm stuck on this:

The documentation currently says the compile-time log files for these 
options are written in "the dump file directory on the user's machine". 
  Where, exactly, is this supposed to be?  From reading the code, it 
looks like the default is the current directory rather than the 
directory of the output file (the default for the -fdump-* options).  Is 
this difference intentional?  If so, can the documentation just say it's 
written to the current directory?  Alternatively, the option that 
controls this, -dumpdir, is not documented in invoke.texi; should it be, 
or is this (and its similarly undocumented friend -dumpbase) strictly an 
internal option for communication between the GCC driver and 
subprocesses, or something like that?

-Sandra