Solaris build requires -D_XOPEN_SOURCE=600 -std=gnu99

Description of problem:

GnuTLS 3.6.8 fails to compile on Solaris i86pc.

Version of gnutls used:

GnuTLS 3.6.8

Distributor of gnutls (e.g., Ubuntu, Fedora, RHEL)

GnuTLS from 3.6.8 source tarball. Fetched from https://www.gnupg.org/ftp/gcrypt/gnutls/v3.6/.

How reproducible:

It is consistently reproducible.

Testing on Solaris 11.3 reveals CFLAGS needs -D_XOPEN_SOURCE=600 -std=gnu99 to avoid some compile errors due to alloca. I believe it is due to the inclusion of Gnulib.

Don't allow -D_XOPEN_SOURCE=600 to cross-pollinate into CXXFLAGS, like by way of CPPFLAGS. -D_XOPEN_SOURCE=600 breaks some C++ features due to the way Solaris enforces standard versions.