modules/pkgconfig: use host machine to calculate install prefix

The `mesonlib.is_*` functions are not correct to use here, since they
are for the build machine, not the host machine. This means if the build
machine if Linux but the host is Haiku, then pkg-config files willb e
installed into $libdir/pkgconfig, instead of $prefix/develop/lib/pkgconfig

mesonbuild/modules/pkgconfig.py

@@ -701,10 +701,11 @@ def parse_variable_list(vardict: T.Dict[str, str]) -> T.List[T.Tuple[str, str]]:
         pcfile = filebase + '.pc'
         pkgroot = pkgroot_name = kwargs['install_dir'] or default_install_dir
         if pkgroot is None:
-            if mesonlib.is_freebsd():
+            m = state.environment.machines.host
+            if m.is_freebsd():
                 pkgroot = os.path.join(_as_str(state.environment.coredata.get_option(OptionKey('prefix'))), 'libdata', 'pkgconfig')
                 pkgroot_name = os.path.join('{prefix}', 'libdata', 'pkgconfig')
-            elif mesonlib.is_haiku():
+            elif m.is_haiku():
                 pkgroot = os.path.join(_as_str(state.environment.coredata.get_option(OptionKey('prefix'))), 'develop', 'lib', 'pkgconfig')
                 pkgroot_name = os.path.join('{prefix}', 'develop', 'lib', 'pkgconfig')
             else: