This commit adds a new config that can be used to specify the target
CXXFLAGS specific to the libstdc++ newlib-nano variant.
By default, this config is set to specify the `-fno-exceptions` option,
which disables C++ exception handling support and greatly reduces the
compiled binary size.
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
7144b5f275