Issue Description:

The README at the top level of the Swift tree suggests the following is needed to build Swift on Linux:

sudo apt-get install git cmake ninja-build clang python uuid-dev libicu-dev icu-devtools libbsd-dev libedit-dev libxml2-dev libsqlite3-dev swig libpython-dev libncurses5-dev pkg-config libblocksruntime-dev libcurl4-openssl-dev

https://github.com/apple/swift/blob/546af19690aa2b2071806add3d710f713fe099d8/README.md#system-requirements

However, it is now necessary to build lib dispatch on Linux when building Foundation, and that has additional dependencies not listed here:

sudo apt-get install autoconf libtool pkg-config clang systemtap-sdt-dev libbsd-dev

https://github.com/apple/swift-corelibs-libdispatch/blob/92773e0ce5faecb1ab3decd4ee6a474b9c877747/INSTALL.md#building-and-installing-for-linux

Ideally the top-level README should list a combination of these so that the user only has to download one set of dependencies to build everything, instead of two separate installations:

sudo apt-get install git cmake ninja-build clang python uuid-dev libicu-dev icu-devtools libbsd-dev libedit-dev libxml2-dev libsqlite3-dev swig libpython-dev libncurses5-dev pkg-config libblocksruntime-dev libcurl4-openssl-dev autoconf libtool systemtap-sdt-dev

https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20161114/003512.html