I also asked the program administrator for our university's cluster, and he reassured that udunits2 is already installed in this library (/usr/include/udunits2/).
install.packages('sf',configure.args=c(sf="--with-udunits2-include=/usr/include/udunits2")
...
Configuration failed because libudunits2.so was not found. Try installing:
* deb: libudunits2-dev (Debian, Ubuntu, ...)
* rpm: udunits2-devel (Fedora, EPEL, ...)
* brew: udunits (OSX)
If udunits2 is already installed in a non-standard location, use:
--configure-args='--with-udunits2-lib=/usr/local/lib'
if the library was not found, and/or:
--configure-args='--with-udunits2-include=/usr/include/udunits2'
if the header was not found, replacing paths with appropriate values.
You can alternatively set UDUNITS2_INCLUDE and UDUNITS2_LIBS manually.