all: remove need for `-fcommon`

Use `extern` where appropriate so that we can remove `-fcommon`
on macOS and others.  On macOS, `-fcommon` generates a number of
linker warnings.

I've tested building on macOS, Linux, FreeBSD, NetBSD, OpenBSD
and illumos.  I am not in a position to test on AIX or other
more esoteric platforms, however.

5 files changed, 126 insertions, 63 deletions

diff --git a/src/cmd/acme/dat.c b/src/cmd/acme/dat.c
new file mode 100644
index 00000000..537f7d75
--- /dev/null
+++ b/src/cmd/acme/dat.c
@@ -0,0 +1,62 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include <thread.h>
+#include <cursor.h>
+#include <mouse.h>
+#include <keyboard.h>
+#include <frame.h>
+#include <fcall.h>
+#include <plumb.h>
+#include <libsec.h>
+#include "dat.h"
+
+uint		globalincref;
+uint		seq;
+uint		maxtab;	/* size of a tab, in units of the '0' character */
+
+Mouse		*mouse;
+Mousectl		*mousectl;
+Keyboardctl	*keyboardctl;
+Reffont		reffont;
+Image		*modbutton;
+Image		*colbutton;
+Image		*button;
+Image		*but2col;
+Image		*but3col;
+Row			row;
+int			timerpid;
+Disk			*disk;
+Text			*seltext;
+Text			*argtext;
+Text			*mousetext;	/* global because Text.close needs to clear it */
+Text			*typetext;		/* global because Text.close needs to clear it */
+Text			*barttext;		/* shared between mousetask and keyboardthread */
+int			bartflag;
+Window		*activewin;
+Column		*activecol;
+Rectangle		nullrect;
+int			fsyspid;
+char			*cputype;
+char			*objtype;
+char			*acmeshell;
+//char			*fontnames[2];
+extern char		wdir[]; /* must use extern because no dimension given */
+int			globalautoindent;
+int			dodollarsigns;
+
+Channel	*cplumb;		/* chan(Plumbmsg*) */
+Channel	*cwait;		/* chan(Waitmsg) */
+Channel	*ccommand;	/* chan(Command*) */
+Channel	*ckill;		/* chan(Rune*) */
+Channel	*cxfidalloc;	/* chan(Xfid*) */
+Channel	*cxfidfree;	/* chan(Xfid*) */
+Channel	*cnewwindow;	/* chan(Channel*) */
+Channel	*mouseexit0;	/* chan(int) */
+Channel	*mouseexit1;	/* chan(int) */
+Channel	*cexit;		/* chan(int) */
+Channel	*cerr;		/* chan(char*) */
+Channel	*cedit;		/* chan(int) */
+Channel	*cwarn;		/* chan(void*)[1] (really chan(unit)[1]) */
+
+QLock	editoutlk;
diff --git a/src/cmd/acme/dat.h b/src/cmd/acme/dat.h
index 03150aa6..8f11d6a3 100644
--- a/src/cmd/acme/dat.h
+++ b/src/cmd/acme/dat.h
@@ -509,53 +509,53 @@ enum	/* editing */
 	Collecting
 };
 
-uint		globalincref;
-uint		seq;
-uint		maxtab;	/* size of a tab, in units of the '0' character */
-
-Display		*display;
-Image		*screen;
-Font			*font;
-Mouse		*mouse;
-Mousectl		*mousectl;
-Keyboardctl	*keyboardctl;
-Reffont		reffont;
-Image		*modbutton;
-Image		*colbutton;
-Image		*button;
-Image		*but2col;
-Image		*but3col;
-Cursor		boxcursor;
-Cursor2		boxcursor2;
-Row			row;
-int			timerpid;
-Disk			*disk;
-Text			*seltext;
-Text			*argtext;
-Text			*mousetext;	/* global because Text.close needs to clear it */
-Text			*typetext;		/* global because Text.close needs to clear it */
-Text			*barttext;		/* shared between mousetask and keyboardthread */
-int			bartflag;
-int			swapscrollbuttons;
-Window		*activewin;
-Column		*activecol;
-Buffer		snarfbuf;
-Rectangle		nullrect;
-int			fsyspid;
-char			*cputype;
-char			*objtype;
-char			*home;
-char			*acmeshell;
-char			*fontnames[2];
-Image		*tagcols[NCOL];
-Image		*textcols[NCOL];
+extern uint		globalincref;
+extern uint		seq;
+extern uint		maxtab;	/* size of a tab, in units of the '0' character */
+
+extern Display		*display;
+extern Image		*screen;
+extern Font			*font;
+extern Mouse		*mouse;
+extern Mousectl		*mousectl;
+extern Keyboardctl	*keyboardctl;
+extern Reffont		reffont;
+extern Image		*modbutton;
+extern Image		*colbutton;
+extern Image		*button;
+extern Image		*but2col;
+extern Image		*but3col;
+extern Cursor		boxcursor;
+extern Cursor2		boxcursor2;
+extern Row			row;
+extern int			timerpid;
+extern Disk			*disk;
+extern Text			*seltext;
+extern Text			*argtext;
+extern Text			*mousetext;	/* global because Text.close needs to clear it */
+extern Text			*typetext;		/* global because Text.close needs to clear it */
+extern Text			*barttext;		/* shared between mousetask and keyboardthread */
+extern int			bartflag;
+extern int			swapscrollbuttons;
+extern Window		*activewin;
+extern Column		*activecol;
+extern Buffer		snarfbuf;
+extern Rectangle		nullrect;
+extern int			fsyspid;
+extern char			*cputype;
+extern char			*objtype;
+extern char			*home;
+extern char			*acmeshell;
+extern char			*fontnames[2];
+extern Image		*tagcols[NCOL];
+extern Image		*textcols[NCOL];
 extern char		wdir[]; /* must use extern because no dimension given */
-int			editing;
-int			erroutfd;
-int			messagesize;		/* negotiated in 9P version setup */
-int			globalautoindent;
-int			dodollarsigns;
-char*		mtpt;
+extern int			editing;
+extern int			erroutfd;
+extern int			messagesize;		/* negotiated in 9P version setup */
+extern int			globalautoindent;
+extern int			dodollarsigns;
+extern char*		mtpt;
 
 enum
 {
@@ -563,20 +563,20 @@ enum
 	Kscrollonedown	= KF|0x21
 };
 
-Channel	*cplumb;		/* chan(Plumbmsg*) */
-Channel	*cwait;		/* chan(Waitmsg) */
-Channel	*ccommand;	/* chan(Command*) */
-Channel	*ckill;		/* chan(Rune*) */
-Channel	*cxfidalloc;	/* chan(Xfid*) */
-Channel	*cxfidfree;	/* chan(Xfid*) */
-Channel	*cnewwindow;	/* chan(Channel*) */
-Channel	*mouseexit0;	/* chan(int) */
-Channel	*mouseexit1;	/* chan(int) */
-Channel	*cexit;		/* chan(int) */
-Channel	*cerr;		/* chan(char*) */
-Channel	*cedit;		/* chan(int) */
-Channel	*cwarn;		/* chan(void*)[1] (really chan(unit)[1]) */
-
-QLock	editoutlk;
+extern Channel	*cplumb;		/* chan(Plumbmsg*) */
+extern Channel	*cwait;		/* chan(Waitmsg) */
+extern Channel	*ccommand;	/* chan(Command*) */
+extern Channel	*ckill;		/* chan(Rune*) */
+extern Channel	*cxfidalloc;	/* chan(Xfid*) */
+extern Channel	*cxfidfree;	/* chan(Xfid*) */
+extern Channel	*cnewwindow;	/* chan(Channel*) */
+extern Channel	*mouseexit0;	/* chan(int) */
+extern Channel	*mouseexit1;	/* chan(int) */
+extern Channel	*cexit;		/* chan(int) */
+extern Channel	*cerr;		/* chan(char*) */
+extern Channel	*cedit;		/* chan(int) */
+extern Channel	*cwarn;		/* chan(void*)[1] (really chan(unit)[1]) */
+
+extern QLock	editoutlk;
 
 #define	STACK	65536
diff --git a/src/cmd/acme/ecmd.c b/src/cmd/acme/ecmd.c
index f7613172..42f79960 100644
--- a/src/cmd/acme/ecmd.c
+++ b/src/cmd/acme/ecmd.c
@@ -19,7 +19,7 @@ char	Enoname[] = "no file name given";
 
 Address	addr;
 File	*menu;
-Rangeset	sel;
+extern Rangeset	sel;
 extern	Text*	curtext;
 Rune	*collection;
 int	ncollection;
diff --git a/src/cmd/acme/mail/mail.c b/src/cmd/acme/mail/mail.c
index e1047bb8..6d051821 100644
--- a/src/cmd/acme/mail/mail.c
+++ b/src/cmd/acme/mail/mail.c
@@ -18,7 +18,7 @@ char *srvname;
 Window	*wbox;
 Message	mbox;
 Message	replies;
-char		*home;
+extern char		*home;
 CFid		*plumbsendfd;
 CFid		*plumbseemailfd;
 CFid		*plumbshowmailfd;
diff --git a/src/cmd/acme/mkfile b/src/cmd/acme/mkfile
index 18bea9e0..ba5877c2 100644
--- a/src/cmd/acme/mkfile
+++ b/src/cmd/acme/mkfile
@@ -25,6 +25,7 @@ OFILES=\
 	util.$O\
 	wind.$O\
 	xfid.$O\
+	dat.$O\
 
 HFILES=dat.h\
 	edit.h\