boost: do not allow context module on sparc

The boost context module does not build on sparc, even if sparc is
advertised as a supported architecture by the boost documentation. So
let's disallow this module for the time being.

Fixes:

  http://autobuild.buildroot.org/results/206/2060e6e31c4d739947097faf6587e0a06681fee2/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/boost/Config.in

@@ -67,11 +67,12 @@ config BR2_PACKAGE_BOOST_CONTAINER
 
 # see
 # http://www.boost.org/doc/libs/1_59_0/libs/context/doc/html/context/architectures.html
-# for the list of supported architectures.
+# for the list of supported architectures. Sparc pretends to be
+# supported, but it doesn't build.
 config BR2_PACKAGE_BOOST_CONTEXT
 	bool "boost-context"
 	depends on (BR2_arm || BR2_armeb || BR2_i386 || BR2_mips || BR2_mipsel \
-			|| BR2_powerpc || BR2_sparc || BR2_x86_64)
+			|| BR2_powerpc || BR2_x86_64)
 
 config BR2_PACKAGE_BOOST_COROUTINE
         bool "boost-coroutine"