wasm: include wasi-libc

This allows CGo code to call some libc functions. Additionally, by
putting memset/memmove/memcpy in an archive they're not included anymore
when not necessary, reducing code size for small programs.

src/runtime/runtime_wasm.go

@@ -2,10 +2,6 @@
 
 package runtime
 
-import (
-	"unsafe"
-)
-
 type timeUnit float64 // time in milliseconds, just like Date.now() in JavaScript
 
 const tickMicros = 1000000
@@ -68,25 +64,3 @@ func ticks() timeUnit
 func abort() {
 	trap()
 }
-
-//go:export memset
-func memset(ptr unsafe.Pointer, c byte, size uintptr) unsafe.Pointer {
-	for i := uintptr(0); i < size; i++ {
-		*(*byte)(unsafe.Pointer(uintptr(ptr) + i)) = c
-	}
-	return ptr
-}
-
-// Implement memmove for LLVM and compiler-rt.
-//go:export memmove
-func libc_memmove(dst, src unsafe.Pointer, size uintptr) unsafe.Pointer {
-	memmove(dst, src, size)
-	return dst
-}
-
-// Implement memcpy for LLVM and compiler-rt.
-//go:export memcpy
-func libc_memcpy(dst, src unsafe.Pointer, size uintptr) unsafe.Pointer {
-	memcpy(dst, src, size)
-	return dst
-}