package/mono: needs NPTL

mono unconditionally uses pthread_attr_get_np and so needs NTPL since
version 4.0.1.43 and
https://github.com/mono/mono/commit/748fefa1d7199f008c6e56499ba482fb17fe1583:

mono-threads-linux.c: In function 'mono_threads_platform_get_stack_bounds':
mono-threads-linux.c:26:15: error: implicit declaration of function 'pthread_getattr_np'; did you mean 'pthread_attr_init'? [-Werror=implicit-function-declaration]
   26 |         res = pthread_getattr_np (pthread_self (), &attr);
      |               ^~~~~~~~~~~~~~~~~~
      |               pthread_attr_init

Fixes:
 - http://autobuild.buildroot.org/results/6534ee4ae699c17ee98f6f89a8a1212936e04481

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 5471d7ce252208ffa8a7cdbb6f1f03939097ba39)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mono/Config.in

@@ -14,7 +14,7 @@ config BR2_PACKAGE_MONO
 	bool "mono"
 	depends on BR2_PACKAGE_MONO_ARCH_SUPPORTS
 	depends on BR2_INSTALL_LIBSTDCPP
-	depends on BR2_TOOLCHAIN_HAS_THREADS
+	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL # pthread_getattr_np()
 	depends on !BR2_STATIC_LIBS
 	select BR2_PACKAGE_LIBATOMIC_OPS
 	help
@@ -23,7 +23,7 @@ config BR2_PACKAGE_MONO
 
 	  http://download.mono-project.com/sources/mono/
 
-comment "mono needs a toolchain w/ C++, threads, dynamic library"
+comment "mono needs a toolchain w/ C++, NPTL, dynamic library"
 	depends on BR2_PACKAGE_MONO_ARCH_SUPPORTS
 	depends on !BR2_INSTALL_LIBSTDCPP || \
-		!BR2_TOOLCHAIN_HAS_THREADS || BR2_STATIC_LIBS
+		!BR2_TOOLCHAIN_HAS_THREADS_NPTL || BR2_STATIC_LIBS