add compiler restriction to C11+

vk1kcm · vk1kcm · commit 04dea054d3be · 2025-06-19T13:15:28.000+10:00
diff --git a/science/xnec2c/Portfile b/science/xnec2c/Portfile
@@ -26,6 +26,7 @@ checksums           rmd160  4cc1d731f8f57c2a785337f9b7a9bbc626007da8 \
                     size    1516554
 
 use_autoreconf      yes
+compiler.c_standard 2011
 
 depends_build-append \
                     port:pkgconfig \
