libc: allow to backtrace out of abort call

Build raise and abort function with dwarf2 info by using
-fasynchronous-unwind-tables to make backtrace() working across a
call to abort.

A scenario where it could be useful is within a signal handler that
wants to dump a backtrace when catching some signal (i.e SIGABRT).
Without having abort & raise built with DWARF2 information, it is not
possible for the libgcc stack unwinder to walk through the call stack
out of the abort/raise function.

Impacts in terms of size are really limited

Current
   text    data     bss     dec     hex filename
    164       0       0     164      a4 ./libpthread/nptl/sysdeps/unix/sysv/linux/raise.os
    164       0       0     164      a4 ./libpthread/nptl/sysdeps/unix/sysv/linux/raise.oS
    220      24       4     248      f8 ./libc/stdlib/abort.os

With (-fasynchronous-unwind-tables)

   text    data     bss     dec     hex filename
    216       0       0     216      d8 ./libpthread/nptl/sysdeps/unix/sysv/linux/raise.os
    216       0       0     216      d8 ./libpthread/nptl/sysdeps/unix/sysv/linux/raise.oS
    280      24       4     308     134 ./libc/stdlib/abort.os

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>
Acked-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/signal/Makefile.in

@@ -24,6 +24,8 @@ ifneq ($(strip $(ARCH_OBJS)),)
 CSRC-y := $(filter-out $(notdir $(ARCH_OBJS:.o=.c)),$(CSRC-y))
 endif
 
+CFLAGS-raise.c = -fasynchronous-unwind-tables
+
 SIGNAL_DIR := $(top_srcdir)libc/signal
 SIGNAL_OUT := $(top_builddir)libc/signal
 

libc/stdlib/Makefile.in

@@ -27,6 +27,8 @@ CSRC-$(if $(findstring yy,$(UCLIBC_HAS_FLOATS)$(UCLIBC_SUSV3_LEGACY)),y) += \
 	gcvt.c
 CSRC-$(UCLIBC_SUSV3_LEGACY) += mktemp.c
 
+CFLAGS-abort.c = -fasynchronous-unwind-tables
+
 # multi source stdlib.c
 CSRC-y += abs.c labs.c atoi.c atol.c strtol.c strtoul.c _stdlib_strto_l.c \
 	qsort.c qsort_r.c bsearch.c \

libpthread/nptl/sysdeps/unix/sysv/linux/Makefile.commonarch

@@ -128,6 +128,8 @@ CFLAGS-timer_gettime.c = -I$(top_srcdir)librt -DIS_IN_librt
 CFLAGS-timer_routines.c = -I$(top_srcdir)librt -DIS_IN_librt
 CFLAGS-timer_settime.c = -I$(top_srcdir)librt -DIS_IN_librt
 
+CFLAGS-raise.c = -fasynchronous-unwind-tables
+
 CFLAGS-linux = -DNOT_IN_libc -DIS_IN_libpthread $(SSP_ALL_CFLAGS)
 
 CFLAGS-OMIT-libc_pthread_init.c = -DNOT_IN_libc -DIS_IN_libpthread