meson: define HAVE_CONFIG_H for the project

meson.build

@@ -144,6 +144,8 @@ libdsm_sources += compat_sources
 
 includes = include_directories('.', 'contrib', 'include', 'compat')
 
+add_project_arguments('-DHAVE_CONFIG_H=1', language: ['c'])
+
 libdsm = library('libdsm',
   libdsm_sources,
   version: meson.project_version(),