[runtimes] Bring back TARGET_TRIPLE

This commit reverts 5099e01568 and 77396bbc98, which broke the build
in various ways. I'm reverting until I can investigate, since that
change appears to be way more subtle than it seemed.

GitOrigin-RevId: 850b57c5fbe7b44d18c9667bb31adfbe307453a6
2 files changed