Fixup devel/hs-c2hs and devel/hs-gtk2hs-buildtools to pass -std=c99 to the preprocessor

The ports using c2hs and gtk2hs fail to build with modern compilers as the c11 features of the FreeBSD system headers are not hidden, yet the tools only understand c99.

• revert change to devel/hs-ncurses from r436451
• patch devel/hs-c2hs to pass -std=c99.
• patch devel/hs-gtk2-buildtools to pass -std=c99.

This should fix compilation of

• devel/hs-ncurses
• dns/hs-gnuidn
• graphics/hs-cairo
• x11-toolkits/hs-vte
• devel/hs-gconf

PR: 216707
Reviewed by: rakuco
Approved by: portmgr (antoine)
Differential Revision: https://reviews.freebsd.org/D10081