Python 3.8 and above fails to build with the IBM XL compiler on Power9 platforms.

## System and Environment Information

```
$ arch
ppc64le
```

```
$ echo $CC
xlc -F/projects/opt/ppc64le/ibm/xlc-16.1.1.7/xlC/16.1.1/etc/xlc.cfg.rhel.7.8.gcc.8.3.0.cuda.10.1
```

```
$ xlc --version
IBM XL C/C++ for Linux, V16.1.1 (5725-C73, 5765-J13)
Version: 16.01.0001.0007
```

## Test Procedure
```
$ git clone git@github.com:quellyn/cpython.git
$ cd cpython
$ checkout 3.8

$ ./configure --with-pydebug
$ make -j2 | tee -a make.out
```

I tested for 3.7, 3.8, 3.9, 3.10, and master. In all cases the `make` failed for versions 3.8+. I've attached both the `config.log` and the make output logs for all. 

- Power9 architecture (ppc64le)
- IBM XL C/C++ 16.1.1.7

Python 3.7 builds without issue.