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Additionally, I've deleted one document which appeared to be outdated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

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@352514 91177308-0d34-0410-b5e6-96231b3b80d8

www/index.html

@@ -26,8 +26,7 @@
     <a href="http://lists.llvm.org/mailman/listinfo/libcxx-dev">libcxx-dev</a>
     <a href="http://lists.llvm.org/mailman/listinfo/libcxx-commits">libcxx-commits</a>
     <a href="http://llvm.org/bugs/">Bug Reports</a>
-    <a href="http://llvm.org/svn/llvm-project/libcxxabi/trunk/">Browse SVN</a>
-    <a href="http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/">Browse ViewVC</a>
+    <a href="https://github.com/llvm/llvm-project/tree/master/libcxxabi/">Browse Sources</a>
   </div>
 </div>
 
@@ -74,29 +73,28 @@ <h2 id="dir-structure">Current Status</h2>
   <h2>Get it and get involved!</h2>
   <!--=====================================================================-->
 
-  <p>To check out the code, use:</p>
+  <p>To check out the code (including llvm and others), use:</p>
 
   <ul>
-  <li><code>svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi</code></li>
+  <li><code>git clone https://github.com/llvm/llvm-project.git</code></li>
   </ul>
 
   <p>To build:</p>
   <ul>
-  <li>Check out libcxxabi into <code>llvm/projects</code></li>
-  <li><code>cd llvm</code></li>
+  <li><code>cd llvm-project</code></li>
   <li><code>mkdir build &amp;&amp; cd build</code></li>
-  <li><code>cmake .. # on linux you may need to prefix with CC=clang CXX=clang++</code></li>
+  <li><code>cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
   <li><code>make</code></li>
   </ul>
 
   <p>To do a standalone build:</p>
   <ul>
   <li>
-    Check out the <a href="http://libcxx.llvm.org">libcxx source</a> tree.
+    Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
   </li>
-  <li><code>cd libcxxabi</code></li>
-  <li><code>mkdir build &amp;&amp; cd build</code></li>
-  <li><code>cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx .. # on
+  <li><code>cd llvm-project</code></li>
+  <li><code>mkdir build-libcxxabi &amp;&amp; cd build-libcxxabi</code></li>
+  <li><code>cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx ../libcxxabi # on
     linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
   <li><code>make</code></li>
   </ul>