Use libdir to install protocols

We pass something like:

meson --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/bin \
--libdir=/usr/x86_64-pc-linux-gnu/lib --libexecdir=/usr/x86_64-pc-linux-gnu/libexec ...

in exherbo, where /usr/lib is symlinked to /usr/$TARGET/lib, /usr/bin -> /usr/$TARGET/bin,
and so on, but before this change they would be installed to /usr/lib, which does not work
since that is a symlink as described above, so use the passed libdir to install protocols.

Author: Jonathon Kowalski

meson.build

@@ -95,9 +95,10 @@ endif
 
 prefixdir = get_option('prefix')
 bindir = join_paths(prefixdir, get_option('bindir'))
+libdir = join_paths(prefixdir, get_option('libdir'))
 datadir = join_paths(prefixdir, get_option('datadir'))
 docdir = join_paths(datadir, 'doc/casync')
-protocoldir = join_paths(prefixdir, 'lib/casync/protocols')
+protocoldir = join_paths(libdir, 'casync/protocols')
 conf.set_quoted('CASYNC_PROTOCOL_PATH', protocoldir)
 
 liblzma = dependency('liblzma',