runtime: correct line numbers for .goc files.

Linenumbers start at 1.
Also call goc2c with an absolute pathi to preserve debug info.

R=rsc, r, ken2
CC=golang-dev
https://golang.org/cl/1954049

src/pkg/runtime/Makefile

@@ -132,7 +132,7 @@ version.go: mkversion
 	./mkversion >version.go
 
 %.c:	%.goc goc2c
-	./goc2c $< > $@.tmp
+	./goc2c `pwd`/$< > $@.tmp
 	mv -f $@.tmp $@
 
 %.$O:	$(GOARCH)/%.c

src/pkg/runtime/goc2c.c

@@ -28,7 +28,7 @@ static int gcc;
 
 /* File and line number */
 static const char *file;
-static unsigned int lineno;
+static unsigned int lineno = 1;
 
 /* List of names and types.  */
 struct params {