wasm: Add a wasm liblc3 library

The wasm library is automatically built when the compiler target
is set to wasm32 in bin/liblc3.wasm.

This can be done using `make CC="clang --target=wasm32"`.

This wasm library doesn't have any import and expose all liblc3
functions.

src/common.h

@@ -24,7 +24,15 @@
 
 #include <stdalign.h>
 #include <limits.h>
+
+#ifdef __wasm32__
+#define memmove __builtin_memmove
+#define memset __builtin_memset
+#define memcpy __builtin_memcpy
+#define NULL ((void*)0)
+#else
 #include <string.h>
+#endif
 
 #ifdef __ARM_ARCH
 #include <arm_acle.h>