package/elf2flt: fix error when building gdb for target on m68k

Thomas reported that m68k fails to build when enabling BR2_PACKAGE_GDB.

It fails when building gdb for the target with the following error:
elf2flt: ERROR: text=0x3c826 overlaps data=0x256e0 ?

It turns out that the gdb binary has another problematic input section
(.gcc_except_table), which causes elf2flt to try to append to the .text
output section, after it has already moved on with appending sections
to the .data output section.

elf2flt cannot append to a previous output section once it has moved on
to another output section.

Update the existing elf2flt patch to also add an exception for
.gcc_except_table.

Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>