Drop the "vsProjectFile" argument from cmTarget::TraceDependencies.  It
appears to be the modern equivalent to a hunk added in commit ba68f771
(...added new custom command support, 2003-06-03):

 +  name = libName;
 +  name += ".dsp.cmake";
 +  srcFilesToProcess.push(name);

but was broken by refactoring at some point.  The current behavior tries
to trace dependencies on a source file named the same as a target, which
makes no sense.  Furthermore, in code of the form

 add_executable(foo foo.c)
 add_custom_command(OUTPUT "${somewhere}/foo" ... DEPENDS foo)

the "vsProjectFile" value "foo" matches source "${somewhere}/foo.rule"
generated to hold the custom command and causes the command to be added
to the "foo" target incorrectly.

Simply drop the incorrect source file trace and supporting logic.