http://wiki.dlang.org/Building_LDC_on_MinGW_x86 for build instructions.
It seems there is a bug in the MinGW TLS support patch linked from that page. This line:
+ DAG.getExternalSymbol("_tls_array"), getPointerTy());
should be
+ DAG.getExternalSymbol("_tls_array", getPointerTy()));
