https://github.com/DaveDavenport/gpx-viewer/commit/c8664e489c7d3982420a505d2bebfbb3bfe8e250

Index: meson.build
--- meson.build.orig
+++ meson.build
@@ -47,6 +47,10 @@ gpx_deps = [
 	meson.get_compiler('c').find_library('m'),
 ]
 
+if dependency ('champlain-0.12', version: '>=0.12.21', required: false).found()
+  add_project_arguments('-D', 'CHAMPLAIN_0_12_21', language: 'vala')
+endif
+
 subdir('libgpx')
 subdir('src')
 
