[pypy-issue] Issue #2811: ropenssl.py incorrectly assumes presence of comp.h (pypy/pypy)

[Dominyk Tiller]

New issue 2811: ropenssl.py incorrectly assumes presence of comp.h
https://bitbucket.org/pypy/pypy/issues/2811/ropensslpy-incorrectly-assumes-presence-of

Dominyk Tiller:

There's an erroneous assumption in `ropenssl.py` that the OpenSSL header `comp.h` will always be available, and consequently when that header isn't available the build can fail:

```
 File "/private/tmp/pypy-20180426-89170-ltfanb/pypy2-v6.0.0-src/rpython/rtyper/tool/rffi_platform.py", line 844, in configure_external_library
    raise last_error
[translation:ERROR] CompilationError: CompilationError(err="""
	/private/tmp/pypy-20180426-89170-ltfanb/pypy2-v6.0.0-src/usession-release-pypy2.7-v6.0.0-0/platcheck_77.c:87:10: fatal error: 'openssl/comp.h' file not found
	#include <openssl/comp.h>
	         ^~~~~~~~~~~~~~~~
	1 error generated.
	""")
```

Whilst it is *usually* available, it is perfectly legitimate to build openssl with `no-comp` passed during compile, which apparently disables installing that header entirely. Homebrew, the macOS package manager, has recently switched its OpenSSL formula to build with `no-comp`, which has revealed this issue.

Normally in C you could wrap the header inclusion in something like `#ifndef OPENSSL_NO_COMP` but I'm not sure how to achieve that in Python.