Revert "toolchain-external: CodeSourcery NiosII 2015.11 affected by PR19405"

An autobuilder exception has been added to avoid testing qt gui module
with the CodeSourcery NiosII toolchain. This allow to remove the
BR2_TOOLCHAIN_HAS_BINUTILS_BUG_19405 symbol.

This reverts commit 5dce3c05.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>