toolbox: turn on -Werror

- Deal with some signedness issues
- Deal with some size issues
- Deal with NULL pointer issues
- Deal with some -Wunused issues

Change-Id: I1479dd90d690084491bae3475f2c547833519a57
diff --git a/toolbox/grep/file.c b/toolbox/grep/file.c
index 86b7658..d28dff5 100644
--- a/toolbox/grep/file.c
+++ b/toolbox/grep/file.c
@@ -78,7 +78,9 @@
 grep_refill(struct file *f)
 {
 	ssize_t nr;
+#ifndef ANDROID
 	int bzerr;
+#endif
 
 	bufpos = buffer;
 	bufrem = 0;