package/gcc: disable gcc D front-end with gcc 12

"The D front-end is now itself written in D, in order to build GDC, you
will need a working GDC compiler (GCC version 9.1 or later)." [1]

So we have to check if a D compiler is available on the host.

Fixes:
http://autobuild.buildroot.org/results/36a/36aa22e458d53ab8687b3a79ffeb65b18e8ac6e7/host-gcc-final-12.1.0/build

[1] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=5fee5ec362f7a243f459e6378fd49dfc89dc9fb5

http://lists.busybox.net/pipermail/buildroot/2022-August/648841.html

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

package/gcc/Config.in.host

@@ -77,6 +77,10 @@ config BR2_GCC_SUPPORTS_DLANG
 	default y if BR2_riscv && !BR2_RISCV_64
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_9
 	depends on BR2_TOOLCHAIN_USES_GLIBC
+	# "The D front-end is now itself written in D, in order to build GDC, you
+	# will need a working GDC compiler (GCC version 9.1 or later)."
+	# https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=5fee5ec362f7a243f459e6378fd49dfc89dc9fb5
+	depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_12
 
 config BR2_GCC_VERSION
 	string