blktrace: add dependency on NPTL

blkiomon.c assumes that clock_nanosleep() is always available. But it
is only available with NPTL. Since it unconditionally uses it, we add
dependency on NPTL.

Fixes:
  http://autobuild.buildroot.net/results/c87/c87cd4a7b0bed938506bcf7e88d4cda60e28e6e5/

Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/blktrace/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_BLKTRACE
 	bool "blktrace"
 	depends on BR2_PACKAGE_LIBAIO_ARCH_SUPPORTS
+	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL # clock_nanosleep()
 	select BR2_PACKAGE_LIBAIO
 	help
 	  blktrace is a block layer IO tracing mechanism which provides
@@ -8,3 +9,7 @@ config BR2_PACKAGE_BLKTRACE
 	  up to user space.
 
 	  http://git.kernel.dk/?p=blktrace.git;a=summary
+
+comment "blktrace needs a toolchain w/ NPTL"
+	depends on BR2_PACKAGE_LIBAIO_ARCH_SUPPORTS
+	depends on !BR2_TOOLCHAIN_HAS_THREADS_NPTL