breaks if no matchpathcon_init_prefix in selinux.h

[Ilya N. Golubev]

Version: 6.12.

If system `selinux/selinux.h' is compilable, coreutils always uses it
(does not build `selinux/selinux.h' in `lib'), and `src/install.c'
assumes that it always provides (correct) declaration of
`matchpathcon_init_prefix'.  If system header does not declare it at
all, build of `ginstall' fails with

undefined reference to `matchpathcon_init_prefix'

Systems with `selinux/selinux.h' causing this failure do exist: ones
with `libselinux-devel-1.23.10-2' (of Fri, 29 Apr 2005 19:27:48 +0000)
as in fedora core 4.  So `matchpathcon_init_prefix' users (including
coreutils) have to at least check that the function exists.

Putting `-DENABLE_MATCHPATHCON=1' in `ginstall_CPPFLAGS' always, even
if no such function exists, also makes little sense.

Fortunately, this provides a workaround of the failure in build
configuration, without changing sources, by putting
`-UENABLE_MATCHPATHCON' in `CPPFLAGS'.