libbacktrace: initial commit

This is a standalone version of the libbacktrace library that I
originally wrote for GCC.  This is a copy of libbacktrace from GCC
trunk, with all dependencies incorporated here.

Makefile.am

@@ -0,0 +1,130 @@
+# Makefile.am -- Backtrace Makefile.
+# Copyright (C) 2012-2016 Free Software Foundation, Inc.
+
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+
+#     (1) Redistributions of source code must retain the above copyright
+#     notice, this list of conditions and the following disclaimer. 
+
+#     (2) Redistributions in binary form must reproduce the above copyright
+#     notice, this list of conditions and the following disclaimer in
+#     the documentation and/or other materials provided with the
+#     distribution.  
+
+#     (3) The name of the author may not be used to
+#     endorse or promote products derived from this software without
+#     specific prior written permission.
+
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+# INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+# STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+# IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+
+AM_CFLAGS = $(EXTRA_FLAGS) $(WARN_FLAGS) $(PIC_FLAG)
+
+lib_LTLIBRARIES = libbacktrace.la
+include_HEADERS = backtrace.h backtrace-supported.h
+
+libbacktrace_la_SOURCES = \
+	backtrace.h \
+	atomic.c \
+	dwarf.c \
+	fileline.c \
+	internal.h \
+	posix.c \
+	print.c \
+	sort.c \
+	state.c
+
+BACKTRACE_FILES = \
+	backtrace.c \
+	simple.c \
+	nounwind.c
+
+FORMAT_FILES = \
+	elf.c \
+	pecoff.c \
+	unknown.c
+
+VIEW_FILES = \
+	read.c \
+	mmapio.c
+
+ALLOC_FILES = \
+	alloc.c \
+	mmap.c
+
+EXTRA_libbacktrace_la_SOURCES = \
+	$(BACKTRACE_FILES) \
+	$(FORMAT_FILES) \
+	$(VIEW_FILES) \
+	$(ALLOC_FILES)
+
+libbacktrace_la_LIBADD = \
+	$(BACKTRACE_FILE) \
+	$(FORMAT_FILE) \
+	$(VIEW_FILE) \
+	$(ALLOC_FILE)
+
+libbacktrace_la_DEPENDENCIES = $(libbacktrace_la_LIBADD)
+
+# Testsuite.
+
+check_PROGRAMS =
+
+TESTS = $(check_PROGRAMS)
+
+if NATIVE
+
+btest_SOURCES = btest.c
+btest_CFLAGS = $(AM_CFLAGS) -g -O
+btest_LDADD = libbacktrace.la
+
+check_PROGRAMS += btest
+
+stest_SOURCES = stest.c
+stest_LDADD = libbacktrace.la
+
+check_PROGRAMS += stest
+
+endif NATIVE
+
+# We can't use automake's automatic dependency tracking, because it
+# breaks when using bootstrap-lean.  Automatic dependency tracking
+# with GCC bootstrap will cause some of the objects to depend on
+# header files in prev-gcc/include, e.g., stddef.h and stdarg.h.  When
+# using bootstrap-lean, prev-gcc is removed after each stage.  When
+# running "make install", those header files will be gone, causing the
+# library to be rebuilt at install time.  That may not succeed.
+
+# These manual dependencies do not include dependencies on unwind.h,
+# even though that is part of GCC, because where to find it depends on
+# whether we are being built as a host library or a target library.
+
+alloc.lo: config.h backtrace.h internal.h
+backtrace.lo: config.h backtrace.h internal.h
+btest.lo: backtrace.h backtrace-supported.h
+dwarf.lo: config.h backtrace.h internal.h
+elf.lo: config.h backtrace.h internal.h
+fileline.lo: config.h backtrace.h internal.h
+mmap.lo: config.h backtrace.h internal.h
+mmapio.lo: config.h backtrace.h internal.h
+nounwind.lo: config.h internal.h
+pecoff.lo: config.h backtrace.h internal.h
+posix.lo: config.h backtrace.h internal.h
+print.lo: config.h backtrace.h internal.h
+read.lo: config.h backtrace.h internal.h
+simple.lo: config.h backtrace.h internal.h
+sort.lo: config.h backtrace.h internal.h
+stest.lo: config.h backtrace.h internal.h
+state.lo: config.h backtrace.h backtrace-supported.h internal.h
+unknown.lo: config.h backtrace.h internal.h