Bug #349130 showed that a missing function declaration can have important side-effects on 64bits architecture because gcc assumes that the return value is 32bits (but if the function returns for example a pointer, the return value will be truncated). The sad thing is that gcc warns about these functions but I found no way to tranforms these warnings into error.

Here's the extract of the build log with all the warning detected:

ea-gnome-calendar.c:186: warning: implicit declaration of function 'e_utf8_strftime'
e-cell-text.c:1362: warning: implicit declaration of function 'gnome_print_pango_create_layout'
e-cell-text.c:1362: warning: assignment makes pointer from integer without a cast
e-cell-text.c:1423: warning: implicit declaration of function 'gnome_print_pango_layout'
e-table-utils.c:116: warning: implicit declaration of function 'strcmp'
e-icon-entry.c:370: warning: implicit declaration of function 'gtk_event_box_new'
e-icon-entry.c:370: warning: assignment makes pointer from integer without a cast
e-icon-entry.c:372: warning: implicit declaration of function 'gtk_event_box_set_visible_window'
e-icon-entry.c:374: warning: implicit declaration of function 'gtk_image_new_from_stock'
e-icon-entry.c:374: warning: assignment makes pointer from integer without a cast
e-minicard.c:850: warning: implicit declaration of function 'e_text_to_html'
e-minicard.c:850: warning: assignment makes pointer from integer without a cast
alarm-notify.c:346: warning: implicit declaration of function ‘e_util_pthread_id’
alarm-notify.c:346: warning: implicit declaration of function ‘pthread_self’
alarm-queue.c:1360: warning: implicit declaration of function ‘gtk_get_current_event_time’
alarm-dialog.c:1081: warning: implicit declaration of function 'gnome_file_entry_set_default_path'
event-page.c:2888: warning: implicit declaration of function 'alarm_list_dialog_peek'
event-page.c:2888: warning: assignment makes pointer from integer without a cast
memo-editor.c:106: warning: implicit declaration of function 'memo_page_set_show_categories'
memo-editor.c:123: warning: implicit declaration of function 'memo_page_set_classification'
calendar-component.c:1380: warning: implicit declaration of function 'gnome_calendar_get_tag'
e-calendar-table.c:1209: warning: implicit declaration of function 'e_cal_model_tasks_mark_task_incomplete'
e-day-view-main-item.c:1443: warning: implicit declaration of function 'draw_curved_rectangle'
e-day-view-top-item.c:928: warning: implicit declaration of function 'draw_curved_rectangle'
e-day-view.c:7159: warning: implicit declaration of function 'e_calendar_view_move_tip'
e-week-view-event-item.c:907: warning: implicit declaration of function 'draw_curved_rectangle'
e-week-view.c:2594: warning: implicit declaration of function 'e_calendar_view_move_tip'
e-msg-composer.c:2856: warning: implicit declaration of function 'gnome_help_display_desktop'
em-folder-view.c:572: warning: implicit declaration of function 'e_filename_make_safe'
em-format-html-display.c:622: warning: implicit declaration of function 'gtk_signal_emit_by_name'
em-format-html-display.c:2344: warning: implicit declaration of function 'e_attachment_bar_create_attachment_cache'