build: avoid redundant bss declarations

Some compilers care, sadly.

R=iant, ken
CC=golang-dev
https://golang.org/cl/4931042

src/Make.inc

@@ -118,7 +118,10 @@ HOST_AR?=ar
 HOST_EXTRA_CFLAGS?=-ggdb -O2
 HOST_EXTRA_LDFLAGS?=
 
-HOST_CFLAGS=-I"$(GOROOT)/include" $(HOST_EXTRA_CFLAGS)
+# The -fno-common here is not necessary, but some compilers
+# on OS X seem to set it by default.  Setting it here keeps the build
+# working in that non-standard context.
+HOST_CFLAGS=-fno-common -I"$(GOROOT)/include" $(HOST_EXTRA_CFLAGS)
 HOST_LDFLAGS=$(HOST_EXTRA_LDFLAGS)
 PWD=$(shell pwd)
 

src/cmd/5c/gc.h

@@ -181,7 +181,7 @@ EXTERN	int32	maxargsafe;
 EXTERN	int	mnstring;
 EXTERN	Multab	multab[20];
 EXTERN	int	retok;
-EXTERN	int	hintabsize;
+extern	int	hintabsize;
 EXTERN	Node*	nodrat;
 EXTERN	Node*	nodret;
 EXTERN	Node*	nodsafe;

src/cmd/5g/gg.h

@@ -5,13 +5,13 @@
 #include <u.h>
 #include <libc.h>
 
-#include "../gc/go.h"
-#include "../5l/5.out.h"
-
 #ifndef	EXTERN
-#define EXTERN	extern
+#define	EXTERN	extern
 #endif
 
+#include "../gc/go.h"
+#include "../5l/5.out.h"
+
 typedef	struct	Addr	Addr;
 
 struct	Addr
@@ -51,22 +51,19 @@ struct	Prog
 #define REGALLOC_F0 (REGALLOC_RMAX+1)
 #define REGALLOC_FMAX (REGALLOC_F0 + FREGEXT)
 
-EXTERN	Biobuf*	bout;
 EXTERN	int32	dynloc;
 EXTERN	uchar	reg[REGALLOC_FMAX+1];
 EXTERN	int32	pcloc;		// instruction counter
 EXTERN	Strlit	emptystring;
 extern	char*	anames[];
-EXTERN	Hist*	hist;
 EXTERN	Prog	zprog;
-EXTERN	Node*	curfn;
 EXTERN	Node*	newproc;
 EXTERN	Node*	deferproc;
 EXTERN	Node*	deferreturn;
 EXTERN	Node*	panicindex;
 EXTERN	Node*	panicslice;
 EXTERN	Node*	throwreturn;
-EXTERN	long	unmappedzero;
+extern	long	unmappedzero;
 EXTERN	int	maxstksize;
 
 /*

src/cmd/5l/softfloat.c

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-#define	EXTERN
 #include	"l.h"
 #include	"../ld/lib.h"
 

src/cmd/6g/gg.h

@@ -5,13 +5,13 @@
 #include <u.h>
 #include <libc.h>
 
-#include "../gc/go.h"
-#include "../6l/6.out.h"
-
 #ifndef	EXTERN
-#define EXTERN	extern
+#define	EXTERN	extern
 #endif
 
+#include "../gc/go.h"
+#include "../6l/6.out.h"
+
 typedef	struct	Addr	Addr;
 
 struct	Addr
@@ -44,22 +44,19 @@ struct	Prog
 	void*	reg;		// pointer to containing Reg struct
 };
 
-EXTERN	Biobuf*	bout;
 EXTERN	int32	dynloc;
 EXTERN	uchar	reg[D_NONE];
 EXTERN	int32	pcloc;		// instruction counter
 EXTERN	Strlit	emptystring;
 extern	char*	anames[];
-EXTERN	Hist*	hist;
 EXTERN	Prog	zprog;
-EXTERN	Node*	curfn;
 EXTERN	Node*	newproc;
 EXTERN	Node*	deferproc;
 EXTERN	Node*	deferreturn;
 EXTERN	Node*	panicindex;
 EXTERN	Node*	panicslice;
 EXTERN	Node*	throwreturn;
-EXTERN	vlong	unmappedzero;
+extern	vlong	unmappedzero;
 
 /*
  * gen.c

src/cmd/6g/reg.c

@@ -29,8 +29,6 @@
 // THE SOFTWARE.
 
 #include "gg.h"
-#undef	EXTERN
-#define	EXTERN
 #include "opt.h"
 
 #define	NREGVAR	32	/* 16 general + 16 floating */

src/cmd/8g/gg.h

@@ -5,13 +5,13 @@
 #include <u.h>
 #include <libc.h>
 
-#include "../gc/go.h"
-#include "../8l/8.out.h"
-
 #ifndef	EXTERN
 #define	EXTERN	extern
 #endif
 
+#include "../gc/go.h"
+#include "../8l/8.out.h"
+
 typedef	struct	Addr	Addr;
 
 struct	Addr
@@ -54,15 +54,12 @@ enum
 	Fpop2 = 1<<2,
 };
 
-EXTERN	Biobuf*	bout;
 EXTERN	int32	dynloc;
 EXTERN	uchar	reg[D_NONE];
 EXTERN	int32	pcloc;		// instruction counter
 EXTERN	Strlit	emptystring;
 extern	char*	anames[];
-EXTERN	Hist*	hist;
 EXTERN	Prog	zprog;
-EXTERN	Node*	curfn;
 EXTERN	Node*	newproc;
 EXTERN	Node*	deferproc;
 EXTERN	Node*	deferreturn;

src/cmd/8g/reg.c

@@ -29,8 +29,6 @@
 // THE SOFTWARE.
 
 #include "gg.h"
-#undef	EXTERN
-#define	EXTERN
 #include "opt.h"
 
 #define	NREGVAR	8

src/cmd/gc/lex.c

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-#define		EXTERN
 #include	"go.h"
 #include	"y.tab.h"
 #include	<ar.h>