Additional default include directory on Tru64 UNIX

[Albert Chin]

The Compaq DTK compiler, the commercial version of the system C
compiler, includes additional header files in /usr/include.dtk. Does
it make sense to add this directory to the default search path for GCC
and for fixincludes if /usr/include.dtk is available? The Compaq DTK
compiler searches includes in /usr/include.dtk before /usr/include.

-- 
albert chin (china@thewrittenword.com)