This update for gcc7 to 7.3 release fixes the following issues:

- Update to GCC 7.3 release and further updated to gcc-7-branch head (r258812).
- Various AArch64 compile fixes are included:

* Picks fix to no longer enable -mpc-relative-literal-loads by default
with --enable-fix-cortex-a53-843419.
* Enable --enable-fix-cortex-a53-843419 for aarch64. [bsc#1084812] [bsc#1087930]
* Enable --enable-fix-cortex-a53-835769 for aarch64.
* Contains fix for PR82445 which is about a RPI1 bootloader miscompile. [bsc#1061667]
* Fixed bogus stack probe instruction on ARM. [bsc#1068967]

- Revert the ios_base::failure ABI back to compatible behavior with the default ABI. [bsc#1087550]

- Fix nvptx offload target compiler install so GCC can pick up
required files. Split out the newlib part into cross-nvptx-newlib7-devel
and avoid conflicts with GCC 8 variant via Provides/Conflicts
of cross-nvptx-newlib-devel.

This update was imported from the SUSE:SLE-12:Update update project.