build-compiler-rt: Signal that sanitizers should use libc++ for the cxxabi parts

This fixes building with the latest master version of compiler-rt,
that uses the itanium cxxabi bits for resolving type info.

build-compiler-rt.sh

@@ -119,6 +119,7 @@ for arch in $ARCHS; do
         -DCMAKE_C_COMPILER_TARGET=$buildarchname-windows-gnu \
         -DCOMPILER_RT_DEFAULT_TARGET_ONLY=TRUE \
         -DCOMPILER_RT_USE_BUILTINS_LIBRARY=TRUE \
+        -DSANITIZER_CXX_ABI=libc++ \
         $SRC_DIR
     $BUILDCMD ${CORES+-j$CORES}
     mkdir -p "$PREFIX/lib/clang/$CLANG_VERSION/lib/windows"