Expose wasm_runtime_call_indirect (#1969)

The function has been there for long. While what it does look a bit unsafe
as it calls a function which may be not wasm-wise exported explicitly, it's
useful and widely used when implementing callback-taking APIs, including
our pthread_create's implementation.

samples/basic/src/native_impl.c

@@ -7,10 +7,6 @@
 #include "wasm_export.h"
 #include "math.h"
 
-extern bool
-wasm_runtime_call_indirect(wasm_exec_env_t exec_env, uint32_t element_indices,
-                           uint32_t argc, uint32_t argv[]);
-
 // The first parameter is not exec_env because it is invoked by native funtions
 void
 reverse(char *str, int len)