Extension of previous commit, only use -Wno-unused-but-set-variable if
GCC version is greater than or equal to 4.5.  This is needed on some
platforms (such as my iMac) to avoid fatal build (gcc) errors.


git-svn-id: svn://irodssvn.ucsd.edu/trunk@5461 ea137bd6-aa86-47b6-b90d-b101d9f19a90