move and deduplicate declarations of __procfdname to make it checkable

syscall.h was chosen as the header to declare it, since its intended
usage is alongside syscalls as a fallback for operations the direct
syscall does not support.

src/internal/procfdname.c

+#include "syscall.h"
+
 void __procfdname(char *buf, unsigned fd)
 {
 	unsigned i, j;

src/internal/syscall.h

@@ -244,4 +244,6 @@ hidden long __syscall_ret(unsigned long), __syscall(syscall_arg_t, ...),
 #define __sys_open_cp(...) __SYSCALL_DISP(__sys_open_cp,,__VA_ARGS__)
 #define sys_open_cp(...) __syscall_ret(__sys_open_cp(__VA_ARGS__))
 
+void __procfdname(char [static 15+3*sizeof(int)], unsigned);
+
 #endif

src/misc/realpath.c

@@ -7,8 +7,6 @@
 #include <string.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 char *realpath(const char *restrict filename, char *restrict resolved)
 {
 	int fd;

src/process/fexecve.c

@@ -4,8 +4,6 @@
 #include <fcntl.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 int fexecve(int fd, char *const argv[], char *const envp[])
 {
 	int r = __syscall(SYS_execveat, fd, "", argv, envp, AT_EMPTY_PATH);

src/stat/fchmod.c

@@ -3,8 +3,6 @@
 #include <fcntl.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 int fchmod(int fd, mode_t mode)
 {
 	int ret = __syscall(SYS_fchmod, fd, mode);

src/stat/fchmodat.c

@@ -3,8 +3,6 @@
 #include <errno.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 int fchmodat(int fd, const char *path, mode_t mode, int flag)
 {
 	if (!flag) return syscall(SYS_fchmodat, fd, path, mode, flag);

src/stat/fstat.c

@@ -4,8 +4,6 @@
 #include "syscall.h"
 #include "libc.h"
 
-void __procfdname(char *, unsigned);
-
 int fstat(int fd, struct stat *st)
 {
 	int ret = __syscall(SYS_fstat, fd, st);

src/unistd/fchdir.c

@@ -3,8 +3,6 @@
 #include <fcntl.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 int fchdir(int fd)
 {
 	int ret = __syscall(SYS_fchdir, fd);

src/unistd/fchown.c

@@ -3,8 +3,6 @@
 #include <fcntl.h>
 #include "syscall.h"
 
-void __procfdname(char *, unsigned);
-
 int fchown(int fd, uid_t uid, gid_t gid)
 {
 	int ret = __syscall(SYS_fchown, fd, uid, gid);

src/unistd/ttyname_r.c

 #include <unistd.h>
 #include <errno.h>
 #include <sys/stat.h>
-
-void __procfdname(char *, unsigned);
+#include "syscall.h"
 
 int ttyname_r(int fd, char *name, size_t size)
 {