encoding.c: Fix -Wmissing-prototypes warnings.

src/libespeak-ng/compiledata.c

 
 #include <espeak-ng/espeak_ng.h>
 #include <espeak-ng/speak_lib.h>
+#include <espeak-ng/encoding.h>
 
 #include "error.h"
 #include "speech.h"
 #include "voice.h"
 #include "synthesize.h"
 #include "spect.h"
+#include "translate.h"
 
 typedef struct {
 	unsigned int value;
 int n_manifest;
 char phsrc[sizeof(path_home)+40]; // Source: path to the 'phonemes' source file.
 
-extern ESPEAK_NG_API int utf8_in(int *c, const char *buf);
-extern int utf8_out(unsigned int c, char *buf);
-
 typedef struct {
 	const char *mnem;
 	int type;

src/libespeak-ng/encoding.c

 #include <espeak-ng/encoding.h>
 
 #include "speech.h"
+#include "phoneme.h"
+#include "voice.h"
+#include "synthesize.h"
+#include "translate.h"
 
 #define LEADING_2_BITS 0xC0 // 0b11000000
 #define UTF8_TAIL_BITS 0x80 // 0b10000000