Fix debug, fuzzer and bazel build

The generated pbzero.h is like:
enum ChromeThreadDescriptor_ThreadType : int32_t {
  ChromeThreadDescriptor_ThreadType_THREAD_UNSPECIFIED = 0,
  ChromeThreadDescriptor_ThreadType_THREAD_MAIN = 1,
..
static const ThreadType THREAD_MAIN = ChromeThreadDescriptor_ThreadType_THREAD_MAIN;
static const ThreadType THREAD_IO = ChromeThreadDescriptor_ThreadType_THREAD_IO;

Nothing defines static storage for those consts in the .cc file (to
keep the .cc file empty and speed up the build).
Somehow aosp/1540890 introduced some "ODR-use" of those
constants that requires static storage.
Falling back on the enum.

Change-Id: I6e9b2a4e079a2d55f967c8b7d5ac604cda5c47f4