Filter out DW.ref.__gxx_personality_v0 in read_symbols.go

As documented, the symbol prefixing mechanism is experimental and
unsupported. There are several corners where we know it doesn't give the
correct output. Nonetheless, this is an easy one to fix.

Fixed: 707
Change-Id: I69a3e61a3198a193cb90f822218f1efbaa31fb1a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/67067
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>

util/read_symbols.go

diff --git a/util/read_symbols.go b/util/read_symbols.go
index 1d8ec85..c5024f4 100644
--- a/util/read_symbols.go
+++ b/util/read_symbols.go
@@ -142,7 +142,7 @@
 				break
 			}
 		}
-		if skip || isCXXSymbol(s) || strings.HasPrefix(s, "__real@") || strings.HasPrefix(s, "__x86.get_pc_thunk.") {
+		if skip || isCXXSymbol(s) || strings.HasPrefix(s, "__real@") || strings.HasPrefix(s, "__x86.get_pc_thunk.") || strings.HasPrefix(s, "DW.") {
 			continue
 		}
 		if _, err := fmt.Fprintln(out, s); err != nil {