The target system might be different from the host system. For example,
you can fuzz Linux binaries compiled for *mipsel*, while your host is
*x86_64*.

Some of the tests depend on specific platforms to run correctly.
For example, the afl-fuzz qemu_mode cmplog test only works on Intel or
ARM systems. The `SYS` variable is populated using `uname -m` and the
test cases then consult this variable to decide whether to run the test
or not.

If you want to test afl-fuzz for qemu_mode on mipsel, you might
want to make sure that Intel or ARM tests don't run. With this
patch, you can supply your own `CPU_TARGET` environment variable and skip
platform specific tests. `SYS` then contains the value of `CPU_TARGET`.

This allows you to add tests for *mipsel* or other niche platforms in
the future as well.

Sample usage:

```
$ cd qemu_mode && env CPU_TARGET=mipsel ./build_qemu_support.sh
$ cd ../test && env CPU_TARGET=mipsel ./test-qemu-mode.sh
[*] Using environment variable CPU_TARGET=mipsel for SYS
[*] starting AFL++ test framework ...
[*] Testing: qemu_mode
...
```

shellcheck pointed out a few command substition (backtick vs. $(...))
and quoting issues. This patch fixes them.

Let user pass their own CPU_TARGET in test-pre.sh

qemuafl now supports persistent mode for *mipsel* targets. This patch
changes the `SYS` variable tests and runs the persistent qemu_mode
tests for *mipsel* as well.

This also adds an optional environment variable called `CPU_TARGET_CC`
that you can pass to the `./test-qemu-mode.sh` test script.

This allows you to specify a cross-compiler for the target platform. The
test script then it uses to compile `test-instr.c` and `test-compcov.c`.

Example usage:

```
CPU_TARGET_CC=mipsel-linux-gnu-cc CPU_TARGET=mipsel ./test-qemu-mode.sh
```

The output should look something like this:

```
[*] Using environment variable CPU_TARGET=mipsel for SYS
[*] starting AFL++ test framework ...
[*] Testing: qemu_mode
[*] Using mipsel-linux-gnu-cc as compiler for target
[*] running afl-fuzz for qemu_mode, this will take approx 10 seconds
[+] afl-fuzz is working correctly with qemu_mode
[*] running afl-fuzz for qemu_mode AFL_ENTRYPOINT, this will take approx 6 seconds
[+] afl-fuzz is working correctly with qemu_mode AFL_ENTRYPOINT
[-] not an intel or arm platform, cannot test qemu_mode compcov
[-] not an intel or arm platform, cannot test qemu_mode cmplog
[*] running afl-fuzz for persistent qemu_mode, this will take approx 10 seconds
[+] afl-fuzz is working correctly with persistent qemu_mode
[+] persistent qemu_mode was noticeable faster than standard qemu_mode
[*] running afl-fuzz for persistent qemu_mode with AFL_QEMU_PERSISTENT_EXITS, this will take approx 10 seconds
[+] afl-fuzz is working correctly with persistent qemu_mode and AFL_QEMU_PERSISTENT_EXITS
[+] persistent qemu_mode with AFL_QEMU_PERSISTENT_EXITS was noticeable faster than standard qemu_mode
[-] we cannot test qemu_mode unsigaction library (32 bit) because it is not present
[+] qemu_mode unsigaction library (64 bit) ignores signals
[*] 1 test cases completed.
[-] not all test cases were executed
[+] all tests were successful :-)
```

This adds a new persistent hook library `mipsel_read_into_a0.c`. With
it, you can test the persistent hook on the *mipsel* architecture.

I'm also updating the README in `utils/qemu_persistent_hook` and
Makefile and explain how to test the persistent hook on *mipsel*.

This all works thanks to qemuafl already having the correct CPU struct
for *mipsel* in `qemuafl/api.h`.

This patch also updates the root `.gitignore` file to ignore the two
test binaries `test` and `mipsel_test`.

Update test code and documentation for afl-fuzz qemu_mode on mipsel

…duling_for_main_fuzzer

WARNF for setting scheduling for main fuzzer instead of FATAL

TODO_verify_il was removed in GCC trunk by 9739ae9384dd7cd3bb1c7683d6b80b7a9116eaf8,
so drop it here.

refactor!: drop python2

instrumentation: drop removed TODO flag from GCC plugins

Modify the UID and GIDs of fuzzing target

qemu_mode/README.persistent.md documents the different base address, but
the test still only had the cases for x86 and x64.

Fix persistent qemu_mode test base address on aarch64

Fix a cmplog rtn instrumentation check if all vectors are empty.

Remove macros for old compiler versions from afl-llvm-* passes

Remove macros for old compiler versions from split-* and injection passes

Remove macros for old compiler versions from sancov passes

…ssing to Nyx)

Patch for Nyx bug in afl-showmap #2