Fix bug where last c flag was ignored

There is currently a check that tries to prevent c-flags that contain
'-' in them from being unintentionally split and included in the list of
commands. For example, we wouldn't want "-fno-exceptions " to appear as
"-fno" and "-exceptions ". The way this check was done was by making sure
the last character of the split string was a space.

This meant that the very last option to appear in the compile command
was ignored (as it doesn't end with a space). This fix explicitly skips
the ends-with-space check on the last option in the command-line.

This isn't the best fix. Really we should be using the same
argument-processing rules as a shell would rather than just splitting on
'-'. That's a much larger and more complicated change though.

autoload/ale/c.vim

@@ -50,12 +50,17 @@ function! ale#c#ParseCFlags(path_prefix, cflag_line) abort
     let l:cflags_list = []
     let l:previous_options = []
 
-    for l:option in split(a:cflag_line, '-')
+    let l:split_lines = split(a:cflag_line, '-')
+    let l:option_index = 0
+
+    while l:option_index < len(l:split_lines)
+        let l:option = l:split_lines[l:option_index]
+        let l:option_index = l:option_index + 1
         call add(l:previous_options, l:option)
         " Check if cflag contained a '-' and should not have been splitted
         let l:option_list = split(l:option, '\zs')
 
-        if len(l:option_list) > 0 && l:option_list[-1] isnot# ' '
+        if len(l:option_list) > 0 && l:option_list[-1] isnot# ' ' && l:option_index < len(l:split_lines)
             continue
         endif
 
@@ -81,7 +86,7 @@ function! ale#c#ParseCFlags(path_prefix, cflag_line) abort
                 call add(l:cflags_list, l:option)
             endif
         endif
-    endfor
+    endwhile
 
     return join(l:cflags_list, ' ')
 endfunction