You may bump into following error when installing packages from AUR:
$ makepkg -si ==> ERROR: options array contains unknown option '!upx'
One workaround is open the
PKGBUILD file, and spot the line which contains
...... options=('staticlibs' 'libtool' '!upx') ......
!upx, then you can build it now.
dropbox: unrecognized !upx in the options array.