[epiphany] Improve libdazzle subproject usage

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 1dc0c97b1ba3cb1b5dc1c8196edd25d2c53637f0
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Aug 7 13:05:24 2018 -0500

    Improve libdazzle subproject usage
    
    We need to pass package_subdir to libdazzle to prevent it from clashing
    with system libdazzle.
    
    Note this is currently broken because there are still clashes. But it
    is less broken than before!

 meson.build | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 7e1ed02a3..15f92801c 100644
--- a/meson.build
+++ b/meson.build
@@ -83,7 +83,7 @@ hogweed_dep = dependency('hogweed', version: nettle_requirement)
 icu_uc_dep = dependency('icu-uc', version: '>= 4.6')
 iso_codes_dep = dependency('iso-codes', version: '>= 0.35')
 json_glib_dep = dependency('json-glib-1.0', version: '>= 1.2.4')
-libdazzle_dep = dependency('libdazzle-1.0', version: '>= 3.29.4', fallback : ['libdazzle', 'libdazzle_dep'])
+libdazzle_dep = dependency('libdazzle-1.0', version: '>= 3.29.4', required: false)
 libnotify_dep = dependency('libnotify', version: '>= 0.5.1')
 libsecret_dep = dependency('libsecret-1', version: '>= 0.14')
 libsoup_dep = dependency('libsoup-2.4', version: '>= 2.48.0')
@@ -94,6 +94,13 @@ sqlite3_dep = dependency('sqlite3', version: '>= 3.0')
 webkit2gtk_dep = dependency('webkit2gtk-4.0', version: webkitgtk_requirement)
 webkit2gtk_web_extension_dep = dependency('webkit2gtk-web-extension-4.0', version: webkitgtk_requirement)
 
+# Ubuntu 18.04 has libdazzle 3.28, the max we can require from the system, but
+# we need 3.30, so bundle it if the system copy is too old.
+if not libdazzle_dep.found()
+  libdazzle_sub = subproject('libdazzle', default_options: ['package_subdir=epiphany'])
+  libdazzle_dep = libdazzle_sub.get_variable('libdazzle_dep')
+endif
+
 cc = meson.get_compiler('c')
 gmp_dep = cc.find_library('gmp')
 m_dep = cc.find_library('m', required: false)