* build-all.sh: Configure with --enable-sjlj-exceptions.
        Build (i.e. implicitly configure) / install libstdc++-v3 after avr-libc.
        * arc-versions.sh (gcc): Change to gcc:avr-gcc-libstdcxx.

Conflicts:
	ChangeLog
	avr-versions.sh
	build-all.sh
        * arc-versions.sh: Update branch names.
        Give more specific error messages when checkout fails.

Conflicts:
	ChangeLog
	avr-versions.sh
Merge branch 'avr-toolchain-libstdcxx-2014' into avr-toolchain-libstdcxx-2014-9

Conflicts:
	ChangeLog
        * avr-versions.sh: Update gcc branch name.
        * run-tests.sh <do_libstdcpp>: Add CFLAGS_FOR_TARGET=-fexceptions to
        runtestflags.
        * run-tests.sh <do_cpp>: Add CFLAGS_FOR_TARGET='-fexceptions -frtti'
        to runtestflags.
Back out change to gcc branch in avr-version.sh merged from
avr-toolchain-libstdcxx-2014-9 .