Log Message:
gcc5-aux, gcc6-aux: patch fixincludes on netbsd.

This is based on an already upstreamed patched that exists in GCC>9.0.
GCC stddef.h relied on the include guards of headers, and those were
changed in netbsd 9.0, so these packages no longer build.

Since we are using a bootstrap GCC, we also need to patch the headers
in the bootstrap fixincludes, patching the package is not sufficient.

Ada part of PR toolchain/54362.