Read .note.gnu.build-id.

This will be used by heapprofd to allow us to correlate build ids with
memory leaks in libraries and binaries.

Test: m
Test: host libunwindstack_test
Test: run unwind_info against my phone's libc.so (32/64) and compare
      to readelf Build ID output.

Bug: 120186412

Change-Id: I3cefd6cce9a8733509bf35b7175eb0f967783477
diff --git a/libunwindstack/tests/ElfFake.h b/libunwindstack/tests/ElfFake.h
index a3bf5ce..c2bd0f6 100644
--- a/libunwindstack/tests/ElfFake.h
+++ b/libunwindstack/tests/ElfFake.h
@@ -72,6 +72,9 @@
 
   bool GetFunctionName(uint64_t, std::string*, uint64_t*) override;
   bool GetGlobalVariable(const std::string&, uint64_t*) override;
+  bool GetBuildID(std::string*) override {
+    return false;
+  }
 
   bool Step(uint64_t, Regs*, Memory*, bool*) override;