package/libudfread: needs __sync_*_4 or threads

libudfread needs __sync_*_4 or threads since its addition in commit
c477885e3f3c31d3922af1fc0e47e6f5f35b1645 and
https://code.videolan.org/videolan/libudfread/-/commit/06c3cb9223a3cb5ab048e42ab353958f422a8f57
to avoid the following build failure:

src/udfread.c:108:3: error: #error no atomic operation support
  108 | # error no atomic operation support
      |   ^~~~~

Fixes:
 - http://autobuild.buildroot.org/results/f76d475f49d525095ac0054224b50b9e612691d6

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

package/libudfread/Config.in

@@ -1,6 +1,10 @@
 config BR2_PACKAGE_LIBUDFREAD
 	bool "libudfread"
+	depends on BR2_TOOLCHAIN_HAS_SYNC_4 || BR2_TOOLCHAIN_HAS_THREADS
 	help
 	  UDF reader
 
 	  https://code.videolan.org/videolan/libudfread
+
+comment "libudfread needs a toolchain w/ threads"
+	depends on !BR2_TOOLCHAIN_HAS_SYNC_4 && !BR2_TOOLCHAIN_HAS_THREADS