xfsprogs: 7.1.0 Build Failure

We're seeing a build failure on AerynOS with 7.1.0 that we didn't get
with 7.0.1:

```
Installing healer-install
../install-sh -o root -g root -m 755 -d /usr/lib/xfsprogs
/usr/bin/dash ../libtool --quiet --mode=install ../install-sh -o root
-g root -m 755 xfs_healer xfs_healer_start /usr/lib/xfsprogs
Usage: /mason/build/x86_64/xfsprogs-7.1.0.tar.xz/libtool [OPTION]...
[MODE-ARG]...
Try 'libtool --help' for more information.
libtool:   error: '/usr/lib/xfsprogs' is not a directory
make[1]: *** [Makefile:72: install-healer] Error 1
```

We use slibtool as our libtool implementation and dash as /usr/bin/sh
so perhaps this is an incompatibility with either of those (likely
slibtool).

It looks like the issue is in `healer/Makefile`. On AerynOS at least
`$(LTINSTALL) -m 755 $(BUILD_TARGETS) $(PKG_LIBEXEC_DIR)` doesn't work
if there are multiple BUILD_TARGETS, and this is the only Makefile
that uses LTINSTALL like that. If I replace it with a loop to install
each target separately the build succeeds as expected.

Regards,
Reilly