FreeBSD works better with static runtimes with g++9

tools/freebsd-gcc-9.dds

@@ -1,9 +1,9 @@
 Compiler-ID: GNU
-C++-Version: C++17
 C-Compiler: gcc9
 C++-Compiler: g++9
 # Range-v3 0.10.0 contains an accidental conversion warning
-Flags: -D SPDLOG_COMPILED_LIB -fconcepts -Werror=return-type -Wno-conversion
+Flags: -D SPDLOG_COMPILED_LIB -Werror=return-type -Wno-conversion
+C++-Flags: -std=c++2a -fconcepts
 Link-Flags: -static-libgcc -static-libstdc++
 Debug:  True
-Compiler-Launcher: ccache
+Compiler-Launcher: ccache