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, 1 deletions

diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 29f9925de16..69a47fcd0fb 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1643,7 +1643,9 @@ impl<'test> TestCx<'test> {
         // double the length.
         let mut f = self.output_base_dir().join("a");
         // FIXME: This is using the host architecture exe suffix, not target!
-        if self.config.target.starts_with("wasm") {
+        if self.config.target.contains("emscripten") {
+            f = f.with_extra_extension("js");
+        } else if self.config.target.starts_with("wasm") {
             f = f.with_extra_extension("wasm");
         } else if self.config.target.contains("spirv") {
             f = f.with_extra_extension("spv");