The libswiftshader_common_debug target adds debug.cpp which uses
utils/String8.h from libutils.

Bug: b/138239233
Change-Id: I7b078e47e56e02d12e44e21a42679a4cd4b6b6df
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36528Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Jason Macnak <natsu@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>