DESTDIR is used for temporary install location
in package managers otherwise you have to add
the temporary locations to BINDIR and LIBDIR
which can cause trouble with the pkg-config file.
The adding of .PHONY caused a silent regression for us, we can just sed it out, but respecting DESTDIR variable will allow a better solution.
Also: make does not take care of whitespaces in $(VAR)
BUILD: respect DESTDIR variable
also at sourceforge https://sourceforge.net/p/glew/patches/41/