Fix Libprocess benchmark OSX

pipe2 does not work on osx.
Replace pipe2 with a helper function that sets up the pipes using pipe()
and then stout/os::cloexec().

Review: https://reviews.apache.org/r/27116
Revert "MESOS-1857 Fixed path::join() on older libstdc++ which lack back()."

This reverts commit ca2e8efcad7d312c6e93acd3546b6811a9f0df19.
Revert "Switched path::join() to be variadic".

This reverts commit b08fccf8f5ea325b8c38055b5f2c03509744dd9b.
Discard label/tag when parsing Version string.

Review: https://reviews.apache.org/r/27115
Add std::unique_ptr and std::move checks to configure script.

Review: https://reviews.apache.org/r/25448
MESOS-1986: Deprecated disabling slave checkpointing.

Review: https://reviews.apache.org/r/27120
MESOS-1712: Automated disallowing of commits mixing
mesos/libprocess/stout.

Review: https://reviews.apache.org/r/26825
Suppressed verbose wget output in support/apply-review.sh.
Moved framework id validation from scheduler driver to master.

Review: https://reviews.apache.org/r/27102
Add --enable-debug and --enable-optimize flag for controlling building debug and optimized verisons of mesos

Reworks buiding mesos in a "debug" vs. a "release" configuration. By default, mesos is built in a developer-centric setup (No optimizations, minimal debug info), in order to maximize developer productivity

None: '-O0 -g1'
--enable-optimize == '-O2'
--enable-debug == '-g'
--enable-optimize --enable-debug == '-O2 -g'

If a user / developer passes CXXFLAGS or CFLAGS manually, then they are not changed / touched at all. This is important so that Mesos is a good citizen when being built for various distributions (As well as making it so specialized one-off groupings of flags are feasible to use).

Adds two defines for accessing what mode things are being built in: 'DEBUG' and 'OPTIMIZE' which can be hooked into later to enable extra logging and the like. For release builds we may want to set 'NDEBUG' which removes assert()'s, but that is a seperate discussion.

Review: https://reviews.apache.org/r/26426