Fixed warnings with gcc option "-Wwrite-strings".

diff --git a/tools/winegcc/utils.c b/tools/winegcc/utils.c
index bd7d7a5..3805a4a 100644
--- a/tools/winegcc/utils.c
+++ b/tools/winegcc/utils.c
@@ -99,7 +99,7 @@
     free(arr);
 }
 
-void strarray_add(strarray* arr, char* str)
+void strarray_add(strarray* arr, const char* str)
 {
     if (arr->size == arr->maximum)
     {
@@ -109,10 +109,10 @@
     arr->base[arr->size++] = str;
 }
 
-void spawn(strarray* arr)
+void spawn(const strarray* arr)
 {
     int i, status;
-    char **argv = arr->base;
+    const char **argv = arr->base;
 
     if (verbose)
     {