is only one boolean setting to enable building strtoll() and strtoull()
port functions. The boolean setting enables the necessary port files
to be built, but the remainder of the logic is via pre-processor code
in the common tif_config.h, which was prepared before entering the
port directory to do a build.
directory and add an include path so that the port files can include
tif_config.h. Do not actually include tif_config.h at this time
since CMake and Autotools builds are not prepared for that. This
issue could be handled by updating the CMake and Autotools builds
or by adding a define which directs libport.h to include tif_config.h.
