Use -Werror in system/core

* Move -Wall -Werror from cppflags to cflags.
* Fix/suppress warning on unused variables.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I1e05e96a1d0bcb2ccef1ce456504b3af57167cc5
1 file changed
tree: a61149dfd4b0cef80eb56fb9d3fd1442c9afd8a8
  1. include/
  2. Android.bp
  3. process.cpp
  4. process_test.cpp