I'm trying to compile and install gcc-4.9.0 on my Debian system, and in particular I want the new version to overwrite an old version of libstdc++.so.6 in /usr/lib/x86_64-linux-gnu that came as standard with my distribution, but which offends various other programs I've installed because it is too old.When I built from source, the configure options I used (with guidance from here) were:configure --prefix=/usr           \          --libdir=/usr/lib       \          --enable-shared         \          --enable-threads=posix  \          --enable-__cxa_atexit   \          --enable-clocale=gnu    \          --disable-multilib      \          --with-system-zlib      \          --enable-languages=c,c++,fortranmake and make install ran successfully; make puts the compiled code into gcc-build/x86_64-unknown-linux-gnu, but unexpectedly make install copies it not into /usr/lib/x86-64-linux-gnu, but into /usr/lib64. What configuration option should I use to get the final version into /usr/lib/x86_64-linuc-gnu?I thought that perhaps the problem was the --disable-multilib option, but when I tried to compile without this I got a configure error to the effect:configure: error: I suspect your system does not have 32-bit developement    libraries (libc and headers). If you have them, rerun configure with --enable-multilib. If you do not have them, and want to build a 64-bit-only compiler, rerun configure with --disable-multilib....so it obviously isn't that.
Install gcc into x86_64-linux-gnu
debian;gcc