Add back old Clangs to Appveyor and Drone

Author: pdimov

.drone.jsonnet

@@ -226,6 +226,20 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "g++-15-multilib",
     ),
 
+    linux_pipeline(
+        "Linux 16.04 Clang 3.5",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.5', CXXSTD: '11' },
+        "clang-3.5",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.6",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.6', CXXSTD: '11,14' },
+        "clang-3.6",
+    ),
+
     linux_pipeline(
         "Linux 16.04 Clang 3.7",
         "cppalliance/droneubuntu1604:1",

appveyor.yml

@@ -21,6 +21,10 @@ environment:
       TOOLSET: msvc-14.1
       CXXSTD: 14,17
       ADDRMD: 32,64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOOLSET: clang-win
+      CXXSTD: 14,17,latest
+      ADDRMD: 64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       TOOLSET: msvc-14.2
       CXXSTD: 14