add and use internal header for *rand48 lcg

src/prng/__rand48_step.c

 #include <stdint.h>
+#include "rand48.h"
 
 uint64_t __rand48_step(unsigned short *xi, unsigned short *lc)
 {

src/prng/__seed48.c

+#include "rand48.h"
+
 unsigned short __seed48[7] = { 0, 0, 0, 0xe66d, 0xdeec, 0x5, 0xb };

src/prng/drand48.c

 #include <stdlib.h>
 #include <inttypes.h>
-
-uint64_t __rand48_step(unsigned short *xi, unsigned short *lc);
-extern unsigned short __seed48[7];
+#include "rand48.h"
 
 double erand48(unsigned short s[3])
 {

src/prng/lcong48.c

 #include <stdlib.h>
 #include <string.h>
-
-extern unsigned short __seed48[7];
+#include "rand48.h"
 
 void lcong48(unsigned short p[7])
 {

src/prng/lrand48.c

 #include <stdlib.h>
 #include <inttypes.h>
-
-uint64_t __rand48_step(unsigned short *xi, unsigned short *lc);
-extern unsigned short __seed48[7];
+#include "rand48.h"
 
 long nrand48(unsigned short s[3])
 {

src/prng/mrand48.c

 #include <stdlib.h>
 #include <inttypes.h>
-
-uint64_t __rand48_step(unsigned short *xi, unsigned short *lc);
-extern unsigned short __seed48[7];
+#include "rand48.h"
 
 long jrand48(unsigned short s[3])
 {

src/prng/rand48.h

+#include <stdint.h>
+
+uint64_t __rand48_step(unsigned short *xi, unsigned short *lc);
+extern unsigned short __seed48[7];

src/prng/seed48.c

 #include <stdlib.h>
 #include <string.h>
-
-extern unsigned short __seed48[7];
+#include "rand48.h"
 
 unsigned short *seed48(unsigned short *s)
 {