ldc ignore mtriple when use with --fsanitize=address

[calvin2021y]

It pass the ldc/bin/../lib/libldc_rt.asan.a to the linker, when I use -mtriple=x86_64-w64-mingw32.

Idc should let the clang to pickup the asan library.

[kinke]

We don't use clang as linker driver on Windows (link.exe or lld-link.exe directly), and don't support MinGW in general either.