archivers/lz4's Makefile varaible collision (OS_VERSION)

[Timo Buhrmester <timo%math.uni-bonn.de@localhost>]

archivers/lz4 will produce (apparently inconsequential) errors while building such as:

| gmake[1]: 10.1: No such file or directory

this is due to their programs/Makefile doing this:

OS_VERSION ?= $(UNAME) -r  # $(UNAME) is "uname"
ifeq ($(TARGET_OS)$(shell $(OS_VERSION)),SunOS5.10)
[...]

i.e. trying to run uname -r, but we already get OS_VERSION="10.1" from the environment, so it ends up trying to run that string.