just run build.sh. run install.sh if u want to install it, but is completely optional, u can run terra directly from terra/install/bin/
if termux crashes/the process get killed by android during compilation or linking problems, idk what causes so, idk how to fix that, but you can edit the build.sh last line from make install -j3 to use more or less cores, see what better fits to your device, going to terra/build and running make install -j3 manually also do the trick sometimes.