Improve stacktraces on Linux/Android standalone debug builds

Improves stacktraces on Linux/Android using libbacktrace.
The library is used only in standalone builds and not shipped
in any official (Chrome or Android) build.
libbacktrace has the advantage of using dwarf info for
symbolization and not requiring to export the dynamic symbol
table (which doesn't work because we have to build with
-fvisibility=hidden because of protobuf)

Bug: 76169489
Change-Id: I308050947c2c57fec630ea94712ee81a5a6543b3
diff --git a/.travis.yml b/.travis.yml
index 69f9cdb..9e94c5a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -106,6 +106,7 @@
     - buildtools/benchmark
     - buildtools/emulator
     - buildtools/googletest
+    - buildtools/libbacktrace
     - buildtools/libcxx
     - buildtools/libcxxabi
     - buildtools/libunwind