meson: fix build definition

Change-Id: I50749a002936da4159be9479f256aa45fce64221

meson.build

@@ -151,7 +151,7 @@ add_project_arguments('-DHAVE_CONFIG_H', language: ['c', 'cpp'])
 #################################################
 # Build targets
 #################################################
-add_project_arguments('-LIBJAMI_BUILD', language: ['c', 'cpp'])
+add_project_arguments('-DLIBJAMI_BUILD', language: ['c', 'cpp'])
 if get_option('default_library') != 'static'
     add_project_arguments('-Djami_EXPORTS', language: ['c', 'cpp'])
 endif