[devhelp] meson: provide Libtool version

[Sébastien Wilmet <swilmet src gnome org>]

commit 16092739072c1cf42b3d8c78efa4111d87c726d0
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sun Mar 11 15:14:25 2018 +0100

    meson: provide Libtool version

 devhelp/meson.build |    5 +++--
 meson.build         |   11 +++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)
---
diff --git a/devhelp/meson.build b/devhelp/meson.build
index 7007b25..3451e72 100644
--- a/devhelp/meson.build
+++ b/devhelp/meson.build
@@ -71,10 +71,11 @@ LIBDEVHELP_STATIC_DEP = declare_dependency(
         dependencies : DEVHELP_DEPS
 )
 
-library(
+shared_library(
         'devhelp-@0@'.format(DEVHELP_API_VERSION),
         link_with : libdevhelp_static,
-        install : true
+        install : true,
+        version : LIBDEVHELP_LT_VERSION
 )
 
 install_headers(
diff --git a/meson.build b/meson.build
index 56c587b..8fabee1 100644
--- a/meson.build
+++ b/meson.build
@@ -14,6 +14,17 @@ GNOME = import('gnome')
 # API version, used for parallel installability.
 DEVHELP_API_VERSION = '3'
 
+# Libtool version numbers, remember to change them just *before* a release.
+# A good time to update it is for the GNOME x.y.90 version, at API freeze,
+# so that packagers have the time to update the package.
+#   (Interfaces removed:    CURRENT++, AGE=0, REVISION=0)
+#   (Interfaces added:      CURRENT++, AGE++, REVISION=0)
+#   (No interfaces changed:                   REVISION++)
+lt_current=5
+lt_revision=0
+lt_age=0
+LIBDEVHELP_LT_VERSION='@0@.@1@.@2@'.format(lt_current, lt_revision, lt_age)
+
 DEVHELP_DEPS = [
         dependency('gio-2.0', version : '>= 2.40'),
         dependency('gtk+-3.0', version : '>= 3.22'),