Bump required enchant to v2, use pkg_check_modules()

Bump the requirement to v2, which means we can remove the
HAVE_ENCHANT_GET_VERSION workaround.

It was released over 8 years ago, with 8 new feature releases since
then and dozens of bugfix releases throughout.

The oldest distributions we target Ubuntu 20.04 and Debian Bullseye,
have 2.2.8 and 2.2.15 respectively.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

src/plugins/CMakeLists.txt

@@ -206,7 +206,7 @@ endif()
 
 if(ENABLE_SPELL)
   if(ENABLE_ENCHANT)
-    find_package(ENCHANT)
+    pkg_check_modules(ENCHANT enchant-2)
     if(ENCHANT_FOUND)
       add_subdirectory(spell)
     else()

src/plugins/spell/CMakeLists.txt

@@ -32,8 +32,8 @@ add_library(spell MODULE
 set_target_properties(spell PROPERTIES PREFIX "")
 
 if(ENCHANT_FOUND)
-  include_directories(${ENCHANT_INCLUDE_DIR})
-  target_link_libraries(spell ${ENCHANT_LIBRARIES} coverage_config)
+  include_directories(${ENCHANT_INCLUDE_DIRS})
+  target_link_libraries(spell ${ENCHANT_LDFLAGS} coverage_config)
   add_definitions(-DUSE_ENCHANT)
 else()
   if(ASPELL_FOUND)

src/plugins/spell/spell.c

@@ -1123,12 +1123,8 @@ spell_debug_libs_cb (const void *pointer, void *data, const char *signal,
     (void) signal_data;
 
 #ifdef USE_ENCHANT
-#ifdef HAVE_ENCHANT_GET_VERSION
     weechat_printf (NULL, "  %s: enchant %s",
                     SPELL_PLUGIN_NAME, enchant_get_version ());
-#else
-    weechat_printf (NULL, "  %s: enchant (?)", SPELL_PLUGIN_NAME);
-#endif /* HAVE_ENCHANT_GET_VERSION */
 #else
 #ifdef HAVE_ASPELL_VERSION_STRING
     weechat_printf (NULL, "  %s: aspell %s",