package/directfb: disable on riscv32

directfb unconditionally uses __NR_futex which will raise the following
build failure on riscv32:

system.c:242:21: error: '__NR_futex' undeclared (first use in this function)
  242 |      ret = syscall( __NR_futex, uaddr, op, val, timeout, uaddr2, val3 );
      |                     ^~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/c0f4168575fa85af933539441eea95a3b10dac91

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/directfb/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_DIRECTFB
 	bool "directfb"
+	depends on !BR2_RISCV_32
 	depends on !BR2_STATIC_LIBS # static link issues
 	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL
 	depends on BR2_INSTALL_LIBSTDCPP
@@ -161,6 +162,7 @@ config BR2_PACKAGE_DIRECTFB_TESTS
 endif # BR2_PACKAGE_DIRECTFB
 
 comment "directfb needs a glibc or uClibc toolchain w/ C++, NPTL, gcc >= 4.5, dynamic library"
+	depends on !BR2_RISCV_32
 	depends on BR2_TOOLCHAIN_HAS_SYNC_4
 	depends on !BR2_TOOLCHAIN_HAS_THREADS_NPTL || !BR2_INSTALL_LIBSTDCPP || \
 		!BR2_TOOLCHAIN_GCC_AT_LEAST_4_5 || BR2_TOOLCHAIN_USES_MUSL || \