[geary] Tidy up inclusion of libunwind in the Meson build.

[Michael Gratton <mjog src gnome org>]

commit 5456dab49c4c5cee944af001c4d8c73dc9b398b1
Author: Michael James Gratton <mike vee net>
Date:   Fri Jan 12 16:05:49 2018 +1100

    Tidy up inclusion of libunwind in the Meson build.
    
    * meson.build: Use libunwind and libunwind-generic to avoid having to
      search for the platform-specific lib.
    
    * src/meson.build: Set UNW_LOCAL_ONLY define to get the most optimal
      unwind impl.

 meson.build     |   11 ++++++-----
 src/meson.build |    3 +++
 2 files changed, 9 insertions(+), 5 deletions(-)
---
diff --git a/meson.build b/meson.build
index 49b7aaa..5874a98 100644
--- a/meson.build
+++ b/meson.build
@@ -63,11 +63,12 @@ javascriptcoregtk_lib = cc.find_library('javascriptcoregtk-4.0', version: '>=' +
 javascriptcoregtk_vapi = valac.find_library('javascriptcore-4.0', dirs: vapi_dir)
 enchant = dependency('enchant', version: '>= 1.6')
 libunwind = declare_dependency(
-  dependencies: [
-    dependency('libunwind', version: '>= 1.1'),
-    cc.find_library('libunwind-' + target_machine.cpu_family()),
-  ],
-)
+   dependencies: [
+     valac.find_library('libunwind', dirs: vapi_dir),
+     cc.find_library('unwind', version: '>= 1.1'),
+     cc.find_library('unwind-generic', version: '>= 1.1'),
+   ],
+ )
 
 libunity = dependency('unity', version: '>= 5.12.0', required: false)
 libmessagingmenu = meson.get_compiler('c').find_library('libmessaging-menu', required: false)
diff --git a/src/meson.build b/src/meson.build
index 103502e..ae1a470 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -24,6 +24,9 @@ endif
 
 geary_c_options = [
   '-include', 'config.h',
+  # Select libunwind's optimised, local-only backtrace unwiding. See
+  # libunwind(3).
+  '-DUNW_LOCAL_ONLY',
   # Vala causes a _lot_ of these to be emitted for otherwise valid
   # code. Suppress them so we can actually see more useful warnings.
   '-Wno-incompatible-pointer-types',