package/liburing: needs MMU

liburing needs MMU since its addition in commit
03ca6f4e39874583060317e7e15e9e360220877e:

setup.c: In function 'io_uring_ring_dontfork':
setup.c:119:8: warning: implicit declaration of function 'madvise'; did you mean 'raise'? [-Wimplicit-function-declaration]
  119 |  ret = madvise(ring->sq.sqes, len, MADV_DONTFORK);
      |        ^~~~~~~
      |        raise

Fixes:
 - http://autobuild.buildroot.org/results/33f3c58e98daab07139b4f400b85f87c0e314240

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/liburing/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_LIBURING
 	bool "liburing"
+	depends on BR2_USE_MMU # madvise()
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9 # C11/stdatomic.h
 	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_1
 	help
@@ -11,5 +12,6 @@ config BR2_PACKAGE_LIBURING
 	  https://git.kernel.dk/cgit/liburing
 
 comment "liburing needs a toolchain w/ gcc >= 4.9, headers >= 5.1"
+	depends on BR2_USE_MMU
 	depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_4_9 || \
 		!BR2_TOOLCHAIN_HEADERS_AT_LEAST_5_1