Bugzilla Bug 139457

$ portageq envvar -v CFLAGS CXXFLAGS
CFLAGS='-O2 -pipe -march=k8 -Wimplicit-function-declaration'
CXXFLAGS='-O2 -pipe -march=k8'

as you can see, i have slightly diff CFLAGS/CXXFLAGS because the warning i use
here isnt valid for C++ ... when building gnash, i see crap like below ... in
other words, the ebuild or build system (i didnt really look) wrongly uses
$CFLAGS for C++ code instead of $CXXFLAGS

x86_64-pc-linux-gnu-g++ -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I. -I.. -I../libbase
-I/usr/include -I/usr/include/SDL -DQT_THREAD_SUPPORT -D_REENTRANT -O2 -pipe
-march=k8 -Wimplicit-function-declaration -ansi -Wall -I/usr/include/SDL -I..
-I. -I.. -I../libbase -I/usr/include -I/usr/include/SDL -O2 -pipe -march=k8
-ansi -Wall -MT tqt.lo -MD -MP -MF .deps/tqt.Tpo -c tqt.cpp  -fPIC -DPIC -o
.libs/tqt.o
cc1plus: warning: command line option "-Wimplicit-function-declaration" is
valid for C/ObjC but not for C++
cc1plus: warning: command line option "-Wimplicit-function-declaration" is
valid for C/ObjC but not for C++

Thanks I made and committed a patch for your issue also reported upstream:
http://savannah.gnu.org/bugs/?func=detailitem&item_id=17049