cranelift: Add heap support to filetest infrastructure (#3154)

* cranelift: Add heap support to filetest infrastructure

* cranelift: Explicit heap pointer placement in filetest annotations

* cranelift: Add documentation about the Heap directive

* cranelift: Clarify that heap filetests pointers must be laid out sequentially

* cranelift: Use wrapping add when computing bound pointer

* cranelift: Better error messages when invalid signatures are found for heap file tests.

cranelift/filetests/src/lib.rs

@@ -34,6 +34,7 @@ pub mod function_runner;
 mod match_directive;
 mod runner;
 mod runone;
+mod runtest_environment;
 mod subtest;
 
 mod test_binemit;