1. install build deps:
$ tce-load -wi libassuan-dev gcr-dev glib2-dev libgpg-error-dev gt k2-dev ncurses-dev ncursesw-dev libsecret-dev m4 qt-5.x-dev texinfo

2. use recommended configure flags from tiny core wiki (for compatibility):
export CFLAGS="-mtune=generic -Os -pipe"
export CXXFLAGS="-mtune=generic -Os -pipe"
export LDFLAGS="-Wl,-O1"

3. the usual
./configure
make
make DESTDIR=/opt/destpinentry-gtk2 install