[Buildroot] [PATCH v2] gcc: Enable __cxa_atexit for final GCC

[Alexey Brodkin]

This is what GCC manual says [1]:
-------------------------->8----------------------
--enable-__cxa_atexit

    Define if you want to use __cxa_atexit, rather than atexit,
    to register C++ destructors for local statics and global objects.

    This is essential for fully standards-compliant handling of destructors,
    but requires __cxa_atexit in libc.

    This option is currently only available on systems with GNU libc
    ...
-------------------------->8----------------------

Important disadvantages of a simple atexit() are that [2]:
-------------------------->8----------------------
1999 C Standard only requires that the implementation support 32
registered functions, although most implementations support many more.

More important it does not deal at all with the ability in most implementations
to remove DSOs from a running program image by calling dlclose
prior to program termination.
-------------------------->8----------------------

Also it seems like all libc's we support in Buildroot (Glibc, uClibc and musl)
support __cxa_at_exit() so enable it unconditionally.

FWIW if we look around we'll see:
 1. In OpenEmbedded it is enabled for everything except gcc-cross-initial: [3], [4]
 2. In Crosstool-NG it is enabled by default: [5]
 3. In OpenWrt it is disabled only for uClibc, otherwise enabled: [6]

So I think we should be good with it as well.

[1] https://gcc.gnu.org/install/configure.html
[2] https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor-motivation
[3] https://github.com/openembedded/openembedded-core/blob/master/meta/recipes-devtools/gcc/gcc-configure-common.inc#L59
[4] https://github.com/openembedded/openembedded-core/blob/master/meta/recipes-devtools/gcc/gcc-cross-initial.inc#L23
[5] https://github.com/crosstool-ng/crosstool-ng/blob/master/config/cc/gcc.in#L270
[6] https://github.com/openwrt/openwrt/blob/master/toolchain/gcc/common.mk#L170

Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
Cc: Nicolas Cavallari <Nicolas.Cavallari at green-communications.fr>
Cc: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
Cc: Mark Corbin <mark.corbin at embecosm.com>
Cc: Romain Naour <romain.naour at gmail.com>
Cc: Peter Korsgaard <peter at korsgaard.com>
Cc: Bernd Kuhls <bernd.kuhls at t-online.de>
Cc: Claudiu Zissulescu <claziss at synopsys.com>
Cc: Cupertino Miranda <cmiranda at synopsys.com>
Cc: Vineet Gupta <vgupta at synopsys.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
---

Changes v1 -> v2:

 * Added references to other buildsystems in commit message
 * Dropped disable in gcc-initial so we have it enabled always

 package/gcc/gcc.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk
index e47435677e..5901624ea5 100644
--- a/package/gcc/gcc.mk
+++ b/package/gcc/gcc.mk
@@ -87,7 +87,7 @@ HOST_GCC_COMMON_DEPENDENCIES = \
 HOST_GCC_COMMON_CONF_OPTS = \
 	--target=$(GNU_TARGET_NAME) \
 	--with-sysroot=$(STAGING_DIR) \
-	--disable-__cxa_atexit \
+	--enable-__cxa_atexit \
 	--with-gnu-ld \
 	--disable-libssp \
 	--disable-multilib \
-- 
2.16.2