compiler: add //go:noheap pragma

src/runtime/runtime.go

@@ -66,6 +66,11 @@ func llvm_sponentry() unsafe.Pointer
 //export strlen
 func strlen(ptr unsafe.Pointer) uintptr
 
+// Special alloc function that should never actually be called.
+// It is used instead of normal alloc in //go:noheap functions, and must either
+// be optimized away or throw a linker error.
+func alloc_noheap(size uintptr, layout unsafe.Pointer) unsafe.Pointer
+
 //export malloc
 func malloc(size uintptr) unsafe.Pointer