Move LD_PRELOAD to a separate test.

The Linux Debug build is currently one of the slowest two, pull out one
phase of it that is independent and allow it to run in parallel with the
other tests.

azure-pipelines.yml

@@ -2,6 +2,50 @@ resources:
 - repo: self
 
 phases:
+- phase: "Linux Self Host"
+  queue:
+    name: 'Hosted Ubuntu 1604'
+
+  steps:
+  - script: |
+      sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+      sudo apt-get update
+      sudo apt-get install -y ninja-build libc++-dev libc++abi-dev libc++abi1 libstdc++-7-dev
+      # sudo apt-get install clang-6.0 clang++-6.0 
+
+      sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-6.0 100
+      sudo update-alternatives --install /usr/bin/cc cc /usr/bin/clang 100
+      sudo update-alternatives --set cc /usr/bin/clang
+
+      sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-6.0 100
+      sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++ 100
+      sudo update-alternatives --set c++ /usr/bin/clang++
+
+    displayName: 'Install Build Dependencies'
+
+  - task: CMake@1
+    displayName: 'CMake .. -GNinja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_FLAGS="-stdlib=libstdc++ -std=c++17"'
+    inputs:
+      cmakeArgs: '.. -GNinja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_FLAGS="-stdlib=libstdc++ -std=c++17"'
+
+  - script: |
+      ninja
+
+    workingDirectory: build
+    failOnStderr: true
+    displayName: 'Compile'
+
+  - script: |
+      sudo cp libsnmallocshim.so /usr/local/lib/
+      sudo cp libsnmallocshim-1mib.so /usr/local/lib/
+      ninja clean
+      LD_PRELOAD=/usr/local/lib/libsnmallocshim.so ninja
+      ninja clean
+      LD_PRELOAD=/usr/local/lib/libsnmallocshim-1mib.so ninja
+    workingDirectory: build
+    failOnStderr: true
+    displayName: 'LD_PRELOAD Compile'
+
 - phase: Linux
   queue:
     name: 'Hosted Ubuntu 1604'
@@ -48,17 +92,6 @@ phases:
     failOnStderr: true
     displayName: 'Test'
 
-  - script: |
-      sudo cp libsnmallocshim.so /usr/local/lib/
-      sudo cp libsnmallocshim-1mib.so /usr/local/lib/
-      ninja clean
-      LD_PRELOAD=/usr/local/lib/libsnmallocshim.so ninja
-      ninja clean
-      LD_PRELOAD=/usr/local/lib/libsnmallocshim-1mib.so ninja
-    workingDirectory: build
-    failOnStderr: true
-    displayName: 'LD_PRELOAD Compile'
-
 - phase: Windows64bit
   queue:
     name: 'Hosted VS2017'