configure.ac: require g++ 4.1 or above

it's known that GCC 4.0 is unable to build LibreOffice;
also remove check for "a buggy version of g++ (3.4.x)"

Change-Id: I97a030c4a214033cab13a69b4c4a599970f9e1cd
Reviewed-on: https://gerrit.libreoffice.org/8812
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>