Config.in: disable Fortify Source for microblaze

As reported by Toolchain-builder project [1], the microblaze glibc
toolchain creates a system that doesn't boot when FORTIFY_SOURCE is
enabled: the init process hangs.

Also, hardening features may not be wanted or possible for such
slow soft-core cpus [2].

Note: for completeness, BR2_RELRO_PARTIAL was manually tested and it
does boot.

[1] https://gitlab.com/bootlin/toolchains-builder/-/jobs/1467624500
[2] http://lists.busybox.net/pipermail/buildroot/2021-June/312416.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

Config.in

@@ -853,9 +853,16 @@ endchoice
 comment "RELocation Read Only (RELRO) needs shared libraries"
 	depends on !BR2_SHARED_LIBS
 
+config BR2_FORTIFY_SOURCE_ARCH_SUPPORTS
+	bool
+	default y
+	# Microblaze glibc toolchains don't work with Fortify Source enabled
+	depends on !BR2_microblaze
+
 choice
 	bool "Buffer-overflow Detection (FORTIFY_SOURCE)"
 	default BR2_FORTIFY_SOURCE_1
+	depends on BR2_FORTIFY_SOURCE_ARCH_SUPPORTS
 	depends on BR2_TOOLCHAIN_USES_GLIBC
 	depends on !BR2_OPTIMIZE_0
 	help
@@ -896,6 +903,7 @@ config BR2_FORTIFY_SOURCE_2
 endchoice
 
 comment "Fortify Source needs a glibc toolchain and optimization"
+	depends on BR2_FORTIFY_SOURCE_ARCH_SUPPORTS
 	depends on (!BR2_TOOLCHAIN_USES_GLIBC || BR2_OPTIMIZE_0)
 endmenu