Removed syntastic and replaced it with ale

Read more here:
https://github.com/w0rp/ale

sources_non_forked/ale/ale_linters/objc/clang.vim

@@ -0,0 +1,23 @@
+" Author: Bang Lee <https://github.com/Qusic>
+" Description: clang linter for objc files
+
+" Set this option to change the Clang options for warnings for ObjC.
+if !exists('g:ale_objc_clang_options')
+    let g:ale_objc_clang_options = '-std=c11 -Wall'
+endif
+
+function! ale_linters#objc#clang#GetCommand(buffer) abort
+    " -iquote with the directory the file is in makes #include work for
+    "  headers in the same directory.
+    return 'clang -S -x objective-c -fsyntax-only '
+    \   . '-iquote ' . ale#Escape(fnamemodify(bufname(a:buffer), ':p:h'))
+    \   . ' ' . ale#Var(a:buffer, 'objc_clang_options') . ' -'
+endfunction
+
+call ale#linter#Define('objc', {
+\   'name': 'clang',
+\   'output_stream': 'stderr',
+\   'executable': 'clang',
+\   'command_callback': 'ale_linters#objc#clang#GetCommand',
+\   'callback': 'ale#handlers#gcc#HandleGCCFormat',
+\})