GCC_EXEC_PREFIX vs jc1

[Bryce McKinlay]

In gcc.c, process_command() appears to attempt to set a value for the
environment variable GCC_EXEC_PREFIX based on the value of argv[0]. The
java compiler later tries to make use of this variable in order to
locate libgcj.zip in a way that works if the installed compiler is later
moved to a different location.

However, process_commands() call to make_relative_prefix() is returning
null on my Red Hat 7.0 system, resulting in this variable never getting
set, and jc1 not being able to find its standard classes.

  [ bryce ]