meson: use jinja2 for the gperf template

Jinja2 inserts an empty line after the first macro body, which I don't know how
to get rid of. Only the first macro causes problems: the other ones don't have
conditional statements at the end and the issue does not occur. As a work-around
I moved ProtectHostname to the end of the first macro.

Output is identical, except for horizontal whitespace and change in position of
ProtectHostname.

src/core/meson.build

@@ -132,9 +132,9 @@ endif
 
 load_fragment_gperf_gperf = custom_target(
         'load-fragment-gperf.gperf',
-        input : 'load-fragment-gperf.gperf.m4',
+        input : 'load-fragment-gperf.gperf.in',
         output: 'load-fragment-gperf.gperf',
-        command : [meson_apply_m4, config_h, '@INPUT@'],
+        command : [meson_render_jinja2, config_h, '@INPUT@'],
         capture : true)
 
 load_fragment_gperf_c = custom_target(