binutils: fix bfin compile error

Newer gcc requires even lower optimization, only with -O0 we
can successfully compile binutils for the target.

Fixes:
  http://autobuild.buildroot.net/results/fb95cd7f7fcc532d036ed8f13853bc6f9a64d1b3

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/binutils/binutils.mk

@@ -64,10 +64,10 @@ HOST_BINUTILS_CONF_ENV += MAKEINFO=true
 HOST_BINUTILS_MAKE_OPTS += MAKEINFO=true
 HOST_BINUTILS_INSTALL_OPTS += MAKEINFO=true install
 
-# gcc bug with Os/O2/O3, PR77311
+# gcc bug with Os/O1/O2/O3, PR77311
 # error: unable to find a register to spill in class 'CCREGS'
 ifeq ($(BR2_bfin),y)
-BINUTILS_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -O1"
+BINUTILS_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -O0"
 endif
 
 # Workaround a build issue with -Os for ARM Cortex-M cpus.