gdb: Pull in Clang -Wincompatible-function-pointer-types handling fix

This commit pulls in the GDB patch that fixes the issue in which
-Wincompatible-function-pointer-types is treated as an error in spite of
having specified --disable-werror when building with Clang.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio