Update LLVM version used on Appveyor bot, remove MSVC 2015 bot

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345652 91177308-0d34-0410-b5e6-96231b3b80d8

appveyor-reqs-install.cmd

@@ -9,7 +9,7 @@ cd C:\projects\deps
 :: Setup Compiler
 ::###########################################################################
 if NOT EXIST llvm-installer.exe (
-  appveyor DownloadFile http://prereleases.llvm.org/win-snapshots/LLVM-7.0.0-r325576-win32.exe -FileName llvm-installer.exe
+  appveyor DownloadFile https://prereleases.llvm.org/win-snapshots/LLVM-8.0.0-r345380-win32.exe -FileName llvm-installer.exe
 )
 if "%CLANG_VERSION%"=="ToT" (
     START /WAIT llvm-installer.exe /S /D=C:\"Program Files\LLVM"

appveyor.yml

@@ -18,14 +18,6 @@ environment:
       GENERATOR: Ninja
       MAKE_PROGRAM: ninja
       APPVEYOR_SAVE_CACHE_ON_ERROR: true
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      CMAKE_OPTIONS: -DCMAKE_C_COMPILER=clang-cl.exe -DCMAKE_CXX_COMPILER=clang-cl.exe
-      CLANG_VERSION: 4
-      MSVC_SETUP_PATH: C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat
-      MSVC_SETUP_ARG: x86_amd64
-      GENERATOR: Ninja
-      MAKE_PROGRAM: ninja
-      APPVEYOR_SAVE_CACHE_ON_ERROR: true
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       MINGW_PATH: C:\mingw-w64\i686-6.3.0-posix-dwarf-rt_v5-rev1\mingw32\bin
       GENERATOR: MinGW Makefiles