Add support for multi-value proposal (#861)

Use the `--enable-multi-value` flag to enable.

A lot of code already "worked" with multi-value, and just needed to
remove the restrictions. Most of the other changes are modifying the
callback APIs to be more general, e.g. taking more than 1 result type.

* Types are now stored as the negative values; this works nicely with
  the encoding of inline function types (used for block signatures),
  which are always positive values.
* Remove `BlockSignature` and use `BlockDeclaration` instead, which
  is just a typedef to `FuncSignature`. This allows for explicit or
  implicit type specifications on the block signatures.
* Allow for >1 "keep" values in the DropKeep interpreter instruction

1 files changed, 11 insertions, 2 deletions

diff --git a/test/parse/expr/bad-loop-sig-multi.txt b/test/parse/expr/bad-loop-sig-multi.txt
index 26bd575e..7763f3d0 100644
--- a/test/parse/expr/bad-loop-sig-multi.txt
+++ b/test/parse/expr/bad-loop-sig-multi.txt
@@ -7,9 +7,18 @@
       i32.const 2
     end
     drop
-    drop))
+    drop)
+
+  (func
+    i32.const 0
+    loop (param i32)
+      drop
+    end))
 (;; STDERR ;;;
-out/test/parse/expr/bad-loop-sig-multi.txt:5:5: error: multiple loop signature result types not currently supported.
+out/test/parse/expr/bad-loop-sig-multi.txt:5:5: error: multiple loop results not currently supported.
     loop (result i32 i32)
     ^^^^
+out/test/parse/expr/bad-loop-sig-multi.txt:14:5: error: loop params not currently supported.
+    loop (param i32)
+    ^^^^
 ;;; STDERR ;;)