Adjust documentation for git migration.

This fixes most references to the paths:
 llvm.org/svn/
 llvm.org/git/
 llvm.org/viewvc/
 github.com/llvm-mirror/
 github.com/llvm-project/
 reviews.llvm.org/diffusion/

to instead point to https://github.com/llvm/llvm-project.

This is *not* a trivial substitution, because additionally, all the
checkout instructions had to be migrated to instruct users on how to
use the monorepo layout, setting LLVM_ENABLE_PROJECTS instead of
checking out various projects into various subdirectories.

I've attempted to not change any scripts here, only documentation. The
scripts will have to be addressed separately.

Additionally, I've deleted one document which appeared to be outdated
and unneeded:
  lldb/docs/building-with-debug-llvm.txt

Differential Revision: https://reviews.llvm.org/D57330

llvm-svn: 352514
diff --git a/llvm/docs/TestingGuide.rst b/llvm/docs/TestingGuide.rst
index 6f24c9d..9908d57 100644
--- a/llvm/docs/TestingGuide.rst
+++ b/llvm/docs/TestingGuide.rst
@@ -165,15 +165,9 @@
 Debugging Information tests
 ---------------------------
 
-To run debugging information tests simply checkout the tests inside
-clang/test directory.
-
-.. code-block:: bash
-
-    % cd clang/test
-    % svn co http://llvm.org/svn/llvm-project/debuginfo-tests/trunk debuginfo-tests
-
-These tests are already set up to run as part of clang regression tests.
+To run debugging information tests simply add the ``debuginfo-tests``
+project to your ``LLVM_ENABLE_PROJECTS`` define on the cmake
+command-line.
 
 Regression test structure
 =========================