Remove autoconf support for building runtime libraries.

Summary:
This patch is provided in preparation for removing autoconf on 1/26. The proposal to remove autoconf on 1/26 was discussed on the llvm-dev thread here: http://lists.llvm.org/pipermail/llvm-dev/2016-January/093875.html

    "I am the punishment of God... If [autoconf] had not committed great sins, God would not have sent a punishment like me upon [it]."
    -Genghis Khan

Reviewers: chandlerc, grosbach, bob.wilson, zaks.anna, kubabrecka, samsonov, echristo

Subscribers: iains, llvm-commits

Differential Revision: http://reviews.llvm.org/D16473

llvm-svn: 258863