Rebase to FSF GDB 8.3.50.20190412 (8.4pre).
Adjust 'gdb-6.3-rh-testversion-20041202.patch'.
Remove 'gdb-follow-child-stale-parent.patch'.
Remove 'gdb-rhbz795424-bitpos-20of25.patch'.
Remove 'gdb-rhbz795424-bitpos-21of25.patch'.
Remove 'gdb-rhbz795424-bitpos-22of25.patch'.
Remove 'gdb-rhbz795424-bitpos-23of25.patch'.
Remove 'gdb-rhbz795424-bitpos-25of25.patch'.
Remove 'gdb-rhbz795424-bitpos-25of25-test.patch'.
Remove 'gdb-rhbz795424-bitpos-arrayview.patch'.
Remove 'gdb-rhbz795424-bitpos-lazyvalue.patch'.
Remove 'gdb-bz541866-rwatch-before-run.patch'.