science/fsom: Fix build on GCC-based architectures

PR:             231693
Submitted by:   Piotr Kubaj <pkubaj@anongoth.pl>
Approved by:    jrm (mentor)
Differential Revision:  https://reviews.freebsd.org/D17366

science/fsom/Makefile

@@ -9,6 +9,7 @@ COMMENT=	Tiny C library for managing SOM (Self-Organizing Maps) neural networks
 
 LICENSE=	GPLv3
 
+USES=		compiler:c++11-lang
 USE_GITHUB=	yes
 GH_ACCOUNT=	ekg
 GH_TAGNAME=	56695e1611d824cda97f08e932d25d08419170cd