Do not use -Wno-psabi warning, not available on old g++

AVR32 uses a very old g++ version, which does not implement the
-Wno-psabi warning flag. This patch simply removes this warning flag
from the libcec build. It can be dropped if only gcc 4.5+ versions are
supported in Buildroot.

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

Index: b/configure.ac
===================================================================
--- a/configure.ac
+++ b/configure.ac
@@ -130,7 +130,7 @@
 use_udev="no"
 use_adapter_detection="yes"
 use_lockdev="no"
-SUPPRESS_MANGLING_WARNINGS=" -Wno-psabi"
+SUPPRESS_MANGLING_WARNINGS=""
 case "${host}" in
   *-*-linux*)
     ## search for udev if pkg-config was found