Update from gcc trunk version of libbacktrace at svn rev 256427. (#8)

Includes (among other things) support for compressed debug sections,
a variety of bugfixes, and expanded test coverage.

internal.h

@@ -1,5 +1,5 @@
 /* internal.h -- Internal header file for stack backtrace library.
-   Copyright (C) 2012-2016 Free Software Foundation, Inc.
+   Copyright (C) 2012-2018 Free Software Foundation, Inc.
    Written by Ian Lance Taylor, Google.
 
 Redistribution and use in source and binary forms, with or without
@@ -268,6 +268,7 @@ extern int backtrace_vector_release (struct backtrace_state *state,
    appropriate one.  */
 
 extern int backtrace_initialize (struct backtrace_state *state,
+				 const char *filename,
 				 int descriptor,
 				 backtrace_error_callback error_callback,
 				 void *data,
@@ -291,4 +292,13 @@ extern int backtrace_dwarf_add (struct backtrace_state *state,
 				backtrace_error_callback error_callback,
 				void *data, fileline *fileline_fn);
 
+/* A test-only hook for elf_uncompress_zdebug.  */
+
+extern int backtrace_uncompress_zdebug (struct backtrace_state *,
+					const unsigned char *compressed,
+					size_t compressed_size,
+					backtrace_error_callback, void *data,
+					unsigned char **uncompressed,
+					size_t *uncompressed_size);
+
 #endif