wasi: remove wasm build tag

The wasm build tag together with GOARCH=arm was causing problems in the
internal/cpu package. In general, I think having two architecture build
tag will only cause problems (in this case, wasm and arm) so I've
removed the wasm build tag and replaced it with tinygo.wasm.

This is similar to the tinygo.riscv build tag, which is used for older
Go versions that don't yet have RISC-V support in the standard library
(and therefore pretend to be GOARCH=arm instead).

src/runtime/arch_tinygowasm.go

@@ -0,0 +1,57 @@
+// +build tinygo.wasm
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+const GOARCH = "wasm"
+
+// The bitness of the CPU (e.g. 8, 32, 64).
+const TargetBits = 32
+
+//go:extern __heap_base
+var heapStartSymbol [0]byte
+
+//go:extern __global_base
+var globalsStartSymbol [0]byte
+
+//export llvm.wasm.memory.size.i32
+func wasm_memory_size(index int32) int32
+
+//export llvm.wasm.memory.grow.i32
+func wasm_memory_grow(index int32, delta int32) int32
+
+var (
+	heapStart    = uintptr(unsafe.Pointer(&heapStartSymbol))
+	heapEnd      = uintptr(wasm_memory_size(0) * wasmPageSize)
+	globalsStart = uintptr(unsafe.Pointer(&globalsStartSymbol))
+	globalsEnd   = uintptr(unsafe.Pointer(&heapStartSymbol))
+)
+
+const wasmPageSize = 64 * 1024
+
+// Align on word boundary.
+func align(ptr uintptr) uintptr {
+	return (ptr + 3) &^ 3
+}
+
+func getCurrentStackPointer() uintptr
+
+// growHeap tries to grow the heap size. It returns true if it succeeds, false
+// otherwise.
+func growHeap() bool {
+	// Grow memory by the available size, which means the heap size is doubled.
+	memorySize := wasm_memory_size(0)
+	result := wasm_memory_grow(0, memorySize)
+	if result == -1 {
+		// Grow failed.
+		return false
+	}
+
+	setHeapEnd(uintptr(wasm_memory_size(0) * wasmPageSize))
+
+	// Heap has grown successfully.
+	return true
+}