toolchain: add support for D language

Since version 9.1, GCC provides support for the D programming language [1].

So add an option to indicate the selected toolchain supports this
language.

[1] https://dlang.org/

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

toolchain/Config.in

@@ -171,6 +171,9 @@ config BR2_ENABLE_LOCALE
 config BR2_INSTALL_LIBSTDCPP
 	bool
 
+config BR2_TOOLCHAIN_HAS_DLANG
+	bool
+
 config BR2_TOOLCHAIN_HAS_FORTRAN
 	bool