split LDLIBS from LDFLAGS to fix link errors in recent toolchains

split LDLIBS from LDFLAGS to fix link errors in recent toolchains

Linker command lines are order-sensitive.
Move linker options -Lfoo -lfoo from LDFLAGS to LDLIBS and place this new
variable after the objects to link. This resolves build errors in xenpagin
and blktap with recent toolchains.

rename SHLIB_CFLAGS to SHLIB_LDFLAGS
rename LDFLAGS_* to LDLIBS_*
move LDFLAGS usage after CFLAGS in CC calls
remove stale comments in xenpaging Makefile

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>