[ASan] Replace CMake if/APPEND/endif with append_if

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@216386 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan/Win] Add /DEBUG to the MD RTL link flags

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@216387 91177308-0d34-0410-b5e6-96231b3b80d8