fix(tests): fix ale_c_build_dir_names being unset in tests (#5109)

- Use ale#Set() to set the ale_c_build_dir_names variable.
- Ensure SetUpLinterTest() is called before any Save commands in tests.
- Add c.vim to runtime before non-linter tests are executed.
- Remove workarounds in c.vim.

autoload/ale/c.vim

@@ -10,7 +10,7 @@ let s:sep = has('win32') ? '\' : '/'
 " Set just so tests can override it.
 let g:__ale_c_project_filenames = ['.git/HEAD', 'configure', 'Makefile', 'CMakeLists.txt']
 
-let g:ale_c_build_dir_names = get(g:, 'ale_c_build_dir_names', [
+call ale#Set('c_build_dir_names', [
 \   'build',
 \   'build/Debug',
 \   'build/Release',
@@ -18,10 +18,6 @@ let g:ale_c_build_dir_names = get(g:, 'ale_c_build_dir_names', [
 \])
 
 function! s:CanParseMakefile(buffer) abort
-    " Something somewhere seems to delete this setting in tests, so ensure we
-    " always have a default value.
-    call ale#Set('c_parse_makefile', 0)
-
     return ale#Var(a:buffer, 'c_parse_makefile')
 endfunction
 
@@ -246,15 +242,6 @@ function! ale#c#FindCompileCommands(buffer) abort
         return [fnamemodify(l:json_file, ':h'), l:json_file]
     endif
 
-    " Something somewhere seems to delete this setting in tests, so ensure
-    " we always have a default value.
-    call ale#Set('c_build_dir_names', [
-    \   'build',
-    \   'build/Debug',
-    \   'build/Release',
-    \   'bin',
-    \])
-
     " Search in build directories if we can't find it in the project.
     for l:path in ale#path#Upwards(expand('#' . a:buffer . ':p:h'))
         for l:dirname in ale#Var(a:buffer, 'c_build_dir_names')