Use -Werror in frameworks/base

* Fix unused variable and return value warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I890e65a20848d00559ba5a4f9691be1347b456af
diff --git a/tools/bit/util.cpp b/tools/bit/util.cpp
index fc93bcb..9223931 100644
--- a/tools/bit/util.cpp
+++ b/tools/bit/util.cpp
@@ -101,7 +101,6 @@
 void
 get_directory_contents(const string& name, map<string,FileInfo>* results)
 {
-    int err;
     DIR* dir = opendir(name.c_str());
     if (dir == NULL) {
         return;
@@ -241,7 +240,9 @@
     fseek(file, 0, SEEK_SET);
 
     char* buf = (char*)malloc(size);
-    fread(buf, 1, size, file);
+    if ((size_t) size != fread(buf, 1, size, file)) {
+        return string();
+    }
 
     string result(buf, size);