cmd/nm: don't add filename elements for m symbols

The compilers used to generate only one 'm' symbol
to record the stack frame size for each function.

In cmd/nm, the 'm' and 'f' symbols are handled in
the same switch case with a special exception for
the symbol described above called ".frame".

Now that the compilers emit additional 'm' symbols
for precise garbage collection of the stack, the
current logic is incorrect. cmd/nm will attempt to
interpret these new 'm' symbols as 'f' symbols and
add them to the file name index table.

This fails with an out-of-memory condition when
zenter encounters an 'm' symbol with a very large
value (usually the .args symbol indicating a
variadic NOSPLIT function).

R=iant
CC=dave, gobot, golang-dev, rsc
https://golang.org/cl/7962045

src/cmd/nm/nm.c

@@ -275,11 +275,13 @@ psym(Sym *s, void* p)
 			return;
 		break;
 	case 'm':
+		if(!aflag || uflag || gflag)
+			return;
+		break;
 	case 'f':	/* we only see a 'z' when the following is true*/
 		if(!aflag || uflag || gflag)
 			return;
-		if (strcmp(s->name, ".frame"))
-			zenter(s);
+		zenter(s);
 		break;
 	case 'a':
 	case 'p':