lib9: fix inconsistencies and warnings on Plan 9

warning: src/lib9/fmt/dorfmt.c:64 unreachable code RETURN
warning: src/lib9/fmt/fltfmt.c:184 set and not used: p
warning: src/lib9/utf/utflen.c:35 unreachable code RETURN
warning: src/lib9/utf/utfrrune.c:45 unreachable code RETURN
warning: src/lib9/utf/utfrune.c:44 unreachable code RETURN

LGTM=rsc
R=rsc, iant, gobot
CC=golang-codereviews
https://golang.org/cl/57170052

src/lib9/errstr.c

+// +build !plan9
+
 /*
 Plan 9 from User Space src/lib9/errstr.c
 http://code.swtch.com/plan9port/src/tip/src/lib9/errstr.c
@@ -32,7 +34,6 @@ THE SOFTWARE.
 
 #include <u.h>
 #include <errno.h>
-#include <string.h>
 #include <libc.h>
 
 enum

src/lib9/fmt/dorfmt.c

@@ -61,5 +61,4 @@ dorfmt(Fmt *f, const Rune *fmt)
 		if(fmt == nil)
 			return -1;
 	}
-	return 0;		/* not reached */
 }

src/lib9/fmt/errfmt.c

+// +build plan9
+
+/*
+ * The authors of this software are Rob Pike and Ken Thompson,
+ * with contributions from Mike Burrows and Sean Dorward.
+ *
+ *     Copyright (c) 2002-2006 by Lucent Technologies.
+ *     Portions Copyright (c) 2004 Google Inc.
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose without fee is hereby granted, provided that this entire notice
+ * is included in all copies of any software which is or includes a copy
+ * or modification of this software and in all copies of the supporting
+ * documentation for such software.
+ * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES 
+ * NOR GOOGLE INC MAKE ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING 
+ * THE MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+ */
+
+#include <u.h>
+#include <libc.h>
+#include "fmtdef.h"
+
+int
+__errfmt(Fmt *f)
+{
+	char buf[ERRMAX];
+
+	rerrstr(buf, sizeof buf);
+	return __fmtcpy(f, buf, utflen(buf), strlen(buf));
+}

src/lib9/fmt/fltfmt.c

@@ -154,6 +154,7 @@ xsub1(char *a, int n)
 	 * so that it has a nonzero first digit.
 	 */
 	abort();
+	return 0;
 }
 
 /*
@@ -180,7 +181,7 @@ xfmtexp(char *p, int e, int ucase)
 		se[i++] = '0';
 	while(i > 0)
 		*p++ = se[--i];
-	*p++ = '\0';
+	*p = '\0';
 }
 
 /*
@@ -192,7 +193,8 @@ xfmtexp(char *p, int e, int ucase)
 static void
 xdtoa(double f, char *s, int *exp, int *neg, int *ns)
 {
-	int d, e2, e, ee, i, ndigit, oerrno;
+	int d, e2, e, ee, i, ndigit;
+	int oerrno;
 	char c;
 	char tmp[NSIGNIF+10];
 	double g;

src/lib9/fmt/fmtfd.c

@@ -43,7 +43,7 @@ fmtfdinit(Fmt *f, int fd, char *buf, int size)
 	f->to = buf;
 	f->stop = buf + size;
 	f->flush = __fmtFdFlush;
-	f->farg = (void*)(uintptr_t)fd;
+	f->farg = (void*)(uintptr)fd;
 	f->flags = 0;
 	f->nfmt = 0;
 	fmtlocaleinit(f, nil, nil, nil);

src/lib9/utf/utfecpy.c

@@ -11,8 +11,8 @@
  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  */
-#define _BSD_SOURCE 1
-#include <string.h>
+#include <u.h>
+#include <libc.h>
 #include "utf.h"
 #include "utfdef.h"
 

src/lib9/utf/utflen.c

@@ -32,5 +32,4 @@ utflen(const char *s)
 			s += chartorune(&rune, s);
 		n++;
 	}
-	return 0;
 }

src/lib9/utf/utfrrune.c

@@ -11,7 +11,8 @@
  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  */
-#include <string.h>
+#include <u.h>
+#include <libc.h>
 #include "utf.h"
 #include "utfdef.h"
 
@@ -42,5 +43,4 @@ utfrrune(const char *s, Rune c)
 			s1 = s;
 		s += c1;
 	}
-	return 0;
 }

src/lib9/utf/utfrune.c

@@ -11,7 +11,8 @@
  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  */
-#include <string.h>
+#include <u.h>
+#include <libc.h>
 #include "utf.h"
 #include "utfdef.h"
 
@@ -41,5 +42,4 @@ utfrune(const char *s, Rune c)
 			return (char*)s;
 		s += n;
 	}
-	return 0;
 }

src/lib9/utf/utfutf.c

@@ -11,7 +11,8 @@
  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  */
-#include <string.h>
+#include <u.h>
+#include <libc.h>
 #include "utf.h"
 #include "utfdef.h"