gcc: bump 4.9 series to 4.9.4

Two patches are removed, as they have been upstreamed:

 - 130-fix_build_with_gcc-6.patch (svn commit 233721, Git commit
   8c3fa311caa86f61b4e28d1563d1110b44340fb2)

 - 920-libgcc-remove-unistd-header.patch (svn commit 226092, Git commit
   e940d7953f06af11d09229a29ecbcc1ba25b378d)

All other patches have simply been refreshed, with no manual edit
needed.

A build+runtime test has been done with an ARM, Cortex-A8, EABIhf, musl
configuration, booted under Qemu.

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