gcc: revert "do not install sys-include headers for cross-compilers."

The change reverts commit 7df4387ebdc9f5293fad04480391e8743c312a3b

A few reasons to revert the commit:
1. The change was not enough to restore `-idirafter` override semantic
   to match unwrapped compiler.
2. The change broke override semantics for cross-compilers
3. The change made override semantics different between cross-compiler
   and native compiler

All of three have some overlap between, but I think it's important
to call all of them out.

The main fallout is the uboot builds, reported by cynerd.

Used the following test to check the override recovery:

    $ nix shell github:NixOS/nixpkgs/release-22.05#pkgsCross.aarch64-multiplatform.stdenv.cc
    $$ cat stdio.h
    # empty
    $$ printf "#include <stdio.h>" | aarch64-unknown-linux-gnu-gcc -E - -o - -idirafter . >/dev/null; echo $?
    0

It failed before the change and succeded after.

0 files changed, 0 insertions, 0 deletions