package/usbguard: disable on musl

usbguard doesn't build on musl because it uses GNU version of strerror_r
as well as basename resulting in the following build failure:

In file included from ./src/Library/public/usbguard/Rule.hpp:24,
                 from src/CLI/usbguard-rule-parser.cpp:23:
./src/Library/public/usbguard/Exception.hpp: In static member function 'static std::string usbguard::ErrnoException::reasonFromErrno(int)':
./src/Library/public/usbguard/Exception.hpp:129:72: error: no matching function for call to 'std::__cxx11::basic_string<char>::basic_string(int)'
  129 |       return std::string(strerror_r(errno_value, buffer, sizeof buffer));
      |

Fixes:
 - http://autobuild.buildroot.org/results/ac1fd7b8c7bd65c73a9213a40c5ed1c39204dab0

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/usbguard/Config.in

@@ -5,6 +5,7 @@ config BR2_PACKAGE_USBGUARD
 	depends on BR2_TOOLCHAIN_HAS_THREADS # libqb, protobuf
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_8 # protobuf
 	depends on !BR2_STATIC_LIBS # libqb, protobuf
+	depends on !BR2_TOOLCHAIN_USES_MUSL
 	select BR2_PACKAGE_PROTOBUF
 	select BR2_PACKAGE_LIBQB
 	help
@@ -16,7 +17,8 @@ config BR2_PACKAGE_USBGUARD
 
 	  https://usbguard.github.io/
 
-comment "usbguard needs a toolchain w/ C++, threads, dynamic library, gcc >= 4.8"
+comment "usbguard needs a glibc or uClibc toolchain w/ C++, threads, dynamic library, gcc >= 4.8"
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS \
-		|| BR2_STATIC_LIBS || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
+		|| BR2_STATIC_LIBS || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8 \
+		|| BR2_TOOLCHAIN_USES_MUSL
 	depends on BR2_PACKAGE_PROTOBUF_ARCH_SUPPORTS