Strange AssertionError with --no-cache-dir

[gst]

Environment

• pip version: 19.0
• Python version: 3.6
• OS: Ubuntu 18.04

Description
Getting AssertionError when installing numpy with --no-cache-dir
NB: it's the same with any package apparently .. :|

Expected behavior
Install succeeds.

How to Reproduce

1. Create a fresh virtualenv : python3 -m virtualenv venv
2. Then run ./venv/bin/pip install --no-cache-dir numpy
3. An error occurs.

Output

gregory.starck@canon:~/tmp$ ./venv/bin/pip install --no-cache-dir numpy 
Looking in indexes: http://pypi:3141/root/ax/+simple/
Collecting numpy
  Downloading http://pypi:3141/root/pypi/+f/2d2/79bd99329e72c/numpy-1.16.0-cp36-cp36m-manylinux1_x86_64.whl (17.3MB)
    100% |████████████████████████████████| 17.3MB 111.4MB/s 
Exception:
Traceback (most recent call last):
  File "/home/gregory.starck/tmp/venv/lib/python3.6/site-packages/pip/_internal/cli/base_command.py", line 176, in main
    status = self.run(options, args)
  File "/home/gregory.starck/tmp/venv/lib/python3.6/site-packages/pip/_internal/commands/install.py", line 346, in run
    session=session, autobuilding=True
  File "/home/gregory.starck/tmp/venv/lib/python3.6/site-packages/pip/_internal/wheel.py", line 848, in build
    assert building_is_possible
AssertionError
gregory.starck@canon:~/tmp$ 

gregory.starck@canon:~/tmp$ ./venv/bin/pip install  numpy 
Looking in indexes: http://pypi:3141/root/ax/+simple/
Collecting numpy
  Downloading http://pypi:3141/root/pypi/+f/2d2/79bd99329e72c/numpy-1.16.0-cp36-cp36m-manylinux1_x86_64.whl (17.3MB)
    100% |████████████████████████████████| 17.3MB 123.5MB/s 
Installing collected packages: numpy
Successfully installed numpy-1.16.0
gregory.starck@canon:~/tmp$ 

[gst]

seems duplicate of #6158

[lock]

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