Add a J2CL compiler script (#7052)

J2CL runs a long pipeline of binaryen opts, including multiple invocations. This adds a
tool that simulates the same process manually, which can be easier to debug with
than running a full J2CL toolchain, which requires Bazel, etc. - this is just a few lines of
bash that does the same thing (at least in simple cases).

scripts/j2cl.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -e
+
+#
+# Simplified version of
+#
+# https://github.com/google/j2cl/blob/e0dee1c7a726952c93d6ace95ddc39c7a6bcc74a/build_defs/internal_do_not_use/j2wasm_application.bzl#L4
+#
+# This can be useful for local testing of issues with j2cl output, by running
+# this instead of setting up a full j2cl toolchain. Usage:
+#
+# j2cl.sh input.wasm output.wasm
+#
+# This will emit one file for each stage of compilation, as output.wasm.N.wasm.
+#
+
+COMMON="--enable-exception-handling --enable-gc --enable-reference-types --enable-sign-ext --enable-strings --enable-nontrapping-float-to-int --enable-bulk-memory --closed-world --traps-never-happen"
+
+echo "Stage 1"
+bin/wasm-opt $COMMON "--no-inline=*_<once>_*" -O3 --cfp-reftest --optimize-j2cl --gufa --unsubtyping -O3 --cfp-reftest --optimize-j2cl -O3 --cfp-reftest --optimize-j2cl $1 -o $2.1.wasm
+
+echo "Stage 2"
+bin/wasm-opt $COMMON  "--no-inline=*_<once>_*" --partial-inlining-ifs=4 -fimfs=25 --gufa --unsubtyping -O3 --cfp-reftest --optimize-j2cl -O3 --cfp-reftest --optimize-j2cl -O3 --cfp-reftest --optimize-j2cl --gufa --unsubtyping -O3 --cfp-reftest --optimize-j2cl -O3 --cfp-reftest --optimize-j2cl $2.1.wasm -o $2.2.wasm
+
+echo "Stage 3"
+bin/wasm-opt $COMMON "--no-full-inline=*_<once>_*" --partial-inlining-ifs=4 --intrinsic-lowering --gufa --unsubtyping -O3 --cfp-reftest --optimize-j2cl -O3 --optimize-j2cl --cfp-reftest --type-merging -O3 --cfp-reftest --optimize-j2cl --string-lowering --remove-unused-module-elements --reorder-globals --type-finalizing $2.2.wasm -o $2.3.wasm 
+