Fix most ui tests on emscripten target

To fix the linker errors, we need to set the output extension to `.js` instead
of `.wasm`. Setting the output to a `.wasm` file puts Emscripten into standalone
mode which is effectively a distinct target. We need to set the runner to be
`node` as well.

This fixes most of the ui tests. I fixed a few more tests with simple problems:
- `intrinsics/intrinsic-alignment.rs` and `structs-enums/rec-align-u64.rs` --
Two `#[cfg]` macros match for Emscripten so we got a duplicate definition of
`mod m`.
- `issues/issue-12699.rs` -- Seems to hang so I disabled it
- `process/process-sigpipe.rs` -- Not expected to work on Emscripten so I
disabled it

1 files changed, 3 insertions, 0 deletions

diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index f768470c4ff..eb571f920df 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -612,6 +612,9 @@ impl Target {
         if triple.contains("-none") || triple.contains("nvptx") || triple.contains("switch") {
             target.no_std = true;
         }
+        if triple.contains("emscripten") {
+            target.runner = Some("node".into());
+        }
         target
     }
 }