Fix #257 in preparation for #427, standardise options with fallbacks, and make it so every value can be computed dynamically

ale_linters/c/cppcheck.vim

@@ -4,12 +4,16 @@
 " Set this option to change the cppcheck options
 let g:ale_c_cppcheck_options = get(g:, 'ale_c_cppcheck_options', '--enable=style')
 
+function! ale_linters#c#cppcheck#GetCommand(buffer) abort
+    return 'cppcheck -q --language=c '
+    \   . g:ale_c_cppcheck_options
+    \   . ' %t'
+endfunction
+
 call ale#linter#Define('c', {
 \   'name': 'cppcheck',
 \   'output_stream': 'both',
 \   'executable': 'cppcheck',
-\   'command': 'cppcheck -q --language=c '
-\       . g:ale_c_cppcheck_options
-\       . ' %t',
+\   'command_callback': 'ale_linters#c#cppcheck#GetCommand',
 \   'callback': 'ale#handlers#HandleCppCheckFormat',
 \})