[gitg] build: Set prefix-relative install_dir for pkgconfig

[Iñigo Martínez <inigomartinez src gnome org>]

commit 0c4f0dd4ac3aefaf189e597d3143f42ee3c1c158
Author: Iñigo Martínez <inigomartinez gmail com>
Date:   Wed Nov 15 17:24:01 2017 +0100

    build: Set prefix-relative install_dir for pkgconfig
    
    While installing seems to have no issues with absolute paths
    for install_dir, the pkgconfig integration in meson does
    and create wrong library paths in the .pc file.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788796

 libgitg-ext/meson.build |    2 +-
 libgitg/meson.build     |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libgitg-ext/meson.build b/libgitg-ext/meson.build
index d71c064..ed03120 100644
--- a/libgitg-ext/meson.build
+++ b/libgitg-ext/meson.build
@@ -68,7 +68,7 @@ libgitg_ext = shared_library(
   link_depends: symbol_map,
   install: true,
   install_dir: [
-    gitg_libdir,
+    get_option('libdir'),
     join_paths(gitg_includedir, lib_api_name, lib_name),
     true,
     true
diff --git a/libgitg/meson.build b/libgitg/meson.build
index bdabb3f..793f2c2 100644
--- a/libgitg/meson.build
+++ b/libgitg/meson.build
@@ -154,7 +154,7 @@ libgitg = shared_library(
   link_depends: symbol_map,
   install: true,
   install_dir: [
-    gitg_libdir,
+    get_option('libdir'),
     join_paths(gitg_includedir, lib_api_name, lib_name),
     true,
     true