Allow building with boost 1.87

Boost for whatever reason added nodiscard on boost::asio::spawn.  Long
term someone likely needs to move this coroutine stuff over to c++20
coroutines, but for now, put in maybe_unused where appropriate.

Change-Id: I72c2039a2bb1e6198a543f89a1820ed3cb78c9df
Signed-off-by: Ed Tanous <ed@tanous.net>
diff --git a/meson.build b/meson.build
index aa6da2a..7e8795a 100644
--- a/meson.build
+++ b/meson.build
@@ -126,7 +126,7 @@
 
 # Dependencies
 
-boost = dependency('boost', modules: ['coroutine'], required: false)
+boost = dependency('boost', modules: ['context', 'coroutine'], required: false)
 
 if not boost.found()
     cmake = import('cmake')