gcc: do not pass --with-pkgversion to gcc < 4.3

Commit 09c181f2 added new options
passed to gcc configure to set --with-pkgversion and --with-bugurl, to
gcc >= gcc 4.3. To check this, it was checking that the GCC_VERSION
string does not contain 4.2.

Unfortunately, the test is bogus. It does a findstring on x4.2. (with
a final dot) but compares the result with x4.2 (without the final
dot).

The result is that even with 4.2 versions, the test was true, leading
--with-pkgversion and --with-bugurl being passed to gcc's configure
script.

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