Respect CXXFLAGS when linking.
hunspell's configure script seems to have been generated with a very old
version of libtool. Specifically, it does not uses CFLAGS instead of
CXXFLAGS when performing some tests related to the C++ compiler.
This ends up making it add '-lstdc++' to the linker's command line even if
one sets CXXFLAGS to -stdlib=libc++. The attached patch fixes the problem by
"backporting" the appropriate libtool.m4 change to the configure script.
Approved by: maintainer timeout (office@, 28 days)