update for c++/3639

[Janis Johnson]

c++/3639 points out a case for which the .bb file produced with
-ftest-coverage has an entry for a line number associated with the
wrong file, which at one time caused gcov to abort.

With GCC 3.0.1 and the mainline, the .bb file still has the same
misleading information but gcov no longer aborts; instead it issues the
message "Unexpected EOF while reading source file x.C" or else reports
call return information in the wrong file.  This is due to a change in
gcov, although I haven't identified which particular change.

The remaining problem is annoying, but not serious since it doesn't
prevent the use of gcov with real C++ applications.

The test case provided in the PR is not preprocessed source, but in
order to demonstrate the problem gcov needs access to the original
source files.  I've submitted a test case that used to cause gcov to
abort and support for testing gcov with C++ in
  http://gcc.gnu.org/ml/gcc-patches/2001-09/msg00684.html
  http://gcc.gnu.org/ml/gcc-patches/2001-09/msg00411.html

Can someone please add this information to GNATS?

Janis