add output redirection to null device for C as well

autoload/syntastic/c.vim

@@ -53,6 +53,17 @@ function! s:Unique(list)
     return l
 endfunction
 
+" convenience function to determine the 'null device' parameter
+" based on the current operating system
+function! syntastic#c#GetNullDevice()
+    if has('win32')
+        return '-o nul'
+    elseif has('unix') || has('mac')
+        return '-o /dev/null'
+    endif
+    return ''
+endfunction
+
 " get the gcc include directory argument depending on the default
 " includes and the optional user-defined 'g:syntastic_c_include_dirs'
 function! syntastic#c#GetIncludeDirs(filetype)

syntax_checkers/c/gcc.vim

@@ -11,7 +11,6 @@
 "============================================================================
 
 " In order to also check header files add this to your .vimrc:
-" (this usually creates a .gch file in your source directory)
 "
 "   let g:syntastic_c_check_header = 1
 "
@@ -108,6 +107,7 @@ function! SyntaxCheckers_c_GetLocList()
         if exists('g:syntastic_c_check_header')
             let makeprg = 'gcc -c '.shellescape(expand('%')) .
                         \ ' ' . g:syntastic_c_compiler_options .
+                        \ ' ' . syntastic#c#GetNullDevice() .
                         \ ' ' . syntastic#c#GetIncludeDirs('c')
         else
             return []

syntax_checkers/cpp.vim

@@ -107,16 +107,9 @@ function! SyntaxCheckers_cpp_GetLocList()
 
     if expand('%') =~? '\%(.h\|.hpp\|.hh\)$'
         if exists('g:syntastic_cpp_check_header')
-            if has('win32')
-                let null_device = '-o nul'
-            elseif has('unix') || has('mac')
-                let null_device = '-o /dev/null'
-            else
-                let null_device = ''
-            endif
             let makeprg = g:syntastic_cpp_compiler.' -c '.shellescape(expand('%')) .
                         \ ' ' . g:syntastic_cpp_compiler_options .
-                        \ ' ' . null_device .
+                        \ ' ' . syntastic#c#GetNullDevice() .
                         \ ' ' . syntastic#c#GetIncludeDirs('cpp')
         else
             return []