[gxml] Improve Meson build and installation

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit 2bc49422178d008095b23da9e9f56a18895425c9
Author: Daniel Espinosa <esodan gmail com>
Date:   Fri Dec 1 23:48:14 2017 -0600

    Improve Meson build and installation
    
    * Installation directory set to default
    * PC file libdir set using a variable prefix

 gxml/meson.build |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gxml/meson.build b/gxml/meson.build
index d6556a8..dadfd75 100644
--- a/gxml/meson.build
+++ b/gxml/meson.build
@@ -5,7 +5,7 @@ VAPI_NAME = VERSIONED_PROJECT_NAME+'.vapi'
 
 conf = configuration_data()
 conf.set('prefix', get_option('prefix'))
-conf.set('libdir', join_paths (get_option ('prefix'),get_option ('libdir')))
+conf.set('libdir', '${exec_prefix}/'+get_option ('libdir'))
 conf.set('VALADEPS', VALADEPS)
 conf.set('PCDEPS', PCDEPS)
 conf.set('PROJECT_NAME', PROJECT_NAME)
@@ -144,7 +144,7 @@ lib = library(VERSIONED_PROJECT_NAME,
        ],
        install : true,
        install_dir : [
-               get_option('libdir'),
+               true,
                join_paths (get_option('includedir'), 'gxml-@0@'.format (API_VERSION), 'gxml'),
                vapidir,
                true