adb: turn on -Werror

- Deal with some -Wunused issues

Change-Id: Idfd1a114e68ae637978b52fde5144d0dca0ec79f
diff --git a/sysdeps_win32.c b/sysdeps_win32.c
index 2105b16..b0cb048 100644
--- a/sysdeps_win32.c
+++ b/sysdeps_win32.c
@@ -956,7 +956,7 @@
             avail = len;
 
         memcpy( bip->buff + bip->a_end, src, avail );
-        src   += avail;
+        src   = (const char *)src + avail;
         count += avail;
         len   -= avail;
 
@@ -1049,7 +1049,7 @@
         avail = len;
 
     memcpy( dst, bip->buff + bip->a_start, avail );
-    dst   += avail;
+    dst   = (char *)dst + avail;
     count += avail;
     len   -= avail;