add -P pkgdir option to 6l to have it look first in pkgdir for a package.

this allows gotest to find the locally built package when doing
	make
	gotest
without this option, one would have to say
	make install
	gotest
which kinda defeats the purpose

based on discussions with rsc.

R=ken,rsc
DELTA=12  (10 added, 1 deleted, 1 changed)
OCL=27606
CL=27606

src/cmd/6l/l.h

@@ -288,6 +288,7 @@ EXTERN	vlong	INITDAT;
 EXTERN	int32	INITRND;
 EXTERN	vlong	INITTEXT;
 EXTERN	char*	INITENTRY;		/* entry point */
+EXTERN	char*	PKGDIR;
 EXTERN	Biobuf	bso;
 EXTERN	int32	bsssize;
 EXTERN	int	cbc;

src/cmd/6l/obj.c

@@ -87,6 +87,7 @@ main(int argc, char *argv[])
 	INITDAT = -1;
 	INITRND = -1;
 	INITENTRY = 0;
+	PKGDIR = nil;
 
 	ARGBEGIN {
 	default:
@@ -122,6 +123,11 @@ main(int argc, char *argv[])
 		if(a)
 			INITRND = atolwhex(a);
 		break;
+	case 'P':
+		a = ARGF();
+		if(a)
+			PKGDIR = a;
+		break;
 	case 'x':	/* produce export table */
 		doexp = 1;
 		if(argv[1] != nil && argv[1][0] != '-' && !isobjfile(argv[1]))
@@ -684,9 +690,10 @@ addlib(char *src, char *obj)
 	}
 
 	if(search) {
-		// try dot and then try goroot.
+		// try dot, -P "pkgdir", and then goroot.
-		// going to have to do better (probably a command line flag) later.
 		snprint(pname, sizeof pname, ".%s", name);
+		if(access(pname, AEXIST) < 0 && PKGDIR != nil)
+			snprint(pname, sizeof pname, "%s/%s", PKGDIR, name);
 		if(access(pname, AEXIST) < 0)
 			snprint(pname, sizeof pname, "%s/pkg/%s", goroot, name);
 		strcpy(name, pname);

src/cmd/gotest/gotest

@@ -13,6 +13,7 @@ GC=${GC:-${O}g}
 GL=${GL:-${O}l}
 export GC GL
 GC="$GC -I _obj"
+GL="$GL -P _obj"
 
 gofiles=""
 loop=true