package/usbguard: needs gcc >= 8

Fix the following build failure raised since the addition of the package
in commit fbff7d7289cc95db991184f890f4ca1fcf8a101e and
https://github.com/USBGuard/usbguard/commit/4b4551023e3298a3639d2c52c559556dbe8d2d54:

checking whether we need to link to -lstdc++fs for PEGTL explicitly... ERROR
configure: error: Link test failed both with and without -lstdc++fs; something is broken, please check file config.log for details.

Fixes:
 - http://autobuild.buildroot.org/results/511c47802ce171caeeb9919371c58e6ad2d11a78

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 442cbf469131fd27d3db7326ff8fc3464cf1b005)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/usbguard/Config.in

@@ -3,7 +3,7 @@ config BR2_PACKAGE_USBGUARD
 	depends on BR2_PACKAGE_PROTOBUF_ARCH_SUPPORTS # protobuf
 	depends on BR2_INSTALL_LIBSTDCPP # protobuf
 	depends on BR2_TOOLCHAIN_HAS_THREADS # libqb, protobuf
-	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_7 # C++17
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_8 # C++17 filesystem
 	depends on !BR2_STATIC_LIBS # libqb, protobuf
 	depends on !BR2_TOOLCHAIN_HAS_GCC_BUG_64735 # std::future
 	select BR2_PACKAGE_PROTOBUF
@@ -18,9 +18,9 @@ config BR2_PACKAGE_USBGUARD
 
 	  https://usbguard.github.io/
 
-comment "usbguard needs a toolchain w/ C++, threads, dynamic library, gcc >= 7"
+comment "usbguard needs a toolchain w/ C++, threads, dynamic library, gcc >= 8"
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS \
-		|| BR2_STATIC_LIBS || !BR2_TOOLCHAIN_GCC_AT_LEAST_7
+		|| BR2_STATIC_LIBS || !BR2_TOOLCHAIN_GCC_AT_LEAST_8
 	depends on BR2_PACKAGE_PROTOBUF_ARCH_SUPPORTS
 
 comment "usbguard needs a toolchain not affected by GCC bug 64735"