libubacktrace: use -asynchronous-funwind-tables rather than -funwind-tables

From gcc documentation, we can read:
" ...
-fasynchronous-unwind-tables
    Generate unwind table in dwarf2 format, if supported by target
    machine. The table is exact at each instruction boundary, so it can be
    used for stack unwinding from asynchronous events (such as debugger or
    garbage collector)
..."

So it seems better rather than using -funwind-tables (glibc seems to prefer
-fasynchronous-unwind-tables).

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>

libubacktrace/Makefile.in

@@ -26,8 +26,8 @@ libubacktrace_OUT := $(top_builddir)libubacktrace
 libubacktrace_SRC-y :=
 libubacktrace_SRC-$(UCLIBC_HAS_BACKTRACE) := backtrace.c backtracesyms.c backtracesymsfd.c
 
-# -funwind-tables is required for backtrace to work using dwarf2
+# -fasynchronous-unwind-tables is required for backtrace to work using dwarf2
-CFLAGS-backtrace.c := -funwind-tables
+CFLAGS-backtrace.c := -fasynchronous-unwind-tables
 
 
 libubacktrace_SRCS := $(addprefix $(libubacktrace_DIR)/,$(libubacktrace_SRC-y))

libubacktrace/backtrace.c

@@ -2,7 +2,7 @@
  * Perform stack unwinding by using the _Unwind_Backtrace.
  *
  * User application that wants to use backtrace needs to be
- * compiled with -funwind-tables option and -rdynamic to get full
+ * compiled with -fasynchronous-unwind-tables option and -rdynamic to get full
  * symbols printed.
  *
  * Copyright (C) 2009, 2010 STMicroelectronics Ltd.