== googletest

googletest is vendored at release-1.8.0-3576-ga05c0915. It was copied
verbatim via git archive and added here.

== libbacktrace

libbacktrace was vendored from github.com/ianlancetaylor/libbacktrace
at commit 793921876c981ce49759114d7bb89bb89b2d3a2d. We dont use its
autotools build infrastructure and integrate it ourselves with mostly
hardcoded config.h and our own Makefile.am bits. Those integration
bits are in libbacktrace-integration in this subdirectory. Main
motivation for such approach is that:

*) we only need symbolization subset

*) we want to avoid polluting global namespace of symbols. We arrange
 for all backtrace symbols to be prefixed tcmalloc_. See
 libbacktrace-integration/config.h.

When updating libbacktrace check that all symbols are renamed by
something like this:

$ make libbacktrace.la
$ objdump -t .libs/libbacktrace.a | grep ' g '

Another notable thing is, we don't bother with mmap support for
reading files metadata and debug info. We actually go to extra length
to replace their alloc.c functions with our own. Our replacement
improves performance some, but most notably it allows us to discard
all the state allocated by libbacktrace. This enables us to not worry
about any synchronization concerns or libbacktrace's lack of ability
to "see" freshly dlopened modules if we did recommended path of doing
thread-ful singleton backtrace state.