science/chemtool-devel: Fix build on FreeBSD 13.1R and 14

• Same fix as 4bfc3a9 for science/chemtool.
• While we are at it, define LICENSE. The license is not shipped, but from the README it is clearly the authors intent to have the same license as for science/chemtool.

while I'm here:

• cleanup Makefile
• remove unnecessary patch and reinplace cmd
• add EXAMPLES option
• add missing LIB_DEPENDS and USE_GNOME deps (Q/A check)
• adopt port

PR: 265614
(cherry picked from commit cb127c6a8da1307a823f638a0489336222bd3f10)