[ASan] Use check_library_exists to determine if libc/libstdc++ are available

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@216264 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan/Win] Land the trivial bits of -MD RTL support (PR20214)

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@216265 91177308-0d34-0410-b5e6-96231b3b80d8
[ubsan] Follow-up for r216263: fix the expected line number.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@216266 91177308-0d34-0410-b5e6-96231b3b80d8