[lit] Honor PYTHONPATH for llvm tests

[greened]

Summary

If the user has a custom PYTHONPATH set, include it in the testing environment. This fixes an issue where certain python packages (pygments, for example) are found during build configuration but then aren't found during testing, leading to test failures.

[thakis]

If we do this, should we do it in lit? Else we probably need to do it in llvm, clang, lld, clang-tools-extra, etc etc etc.

[greened]

In D58546#1407441, @thakis wrote:

If we do this, should we do it in lit? Else we probably need to do it in llvm, clang, lld, clang-tools-extra, etc etc etc.

Maybe? I did just enough to get tests working for us. It would be helpful to get this merged before tackling the larger lit question.

[serge-sans-paille]

I'd rather have it here than in lit. As a test environment, I love it when there's as few environment values that depends on the launch site as possible. It makes reproducibility easier.

llvm/test/lit.cfg.py

 
 llvm_config.with_system_environment('CAML_LD_LIBRARY_PATH')
 llvm_config.with_environment(
     'CAML_LD_LIBRARY_PATH', llvm_ocaml_lib, append_path=True)
 
 # Set up OCAMLRUNPARAM to enable backtraces in OCaml tests.
 llvm_config.with_environment('OCAMLRUNPARAM', 'b')
 
+# Honor PYTHONPATH if set.
+llvm_config.with_system_environment('PYTHONPATH')
+
 # Provide the path to asan runtime lib 'libclang_rt.asan_osx_dynamic.dylib' if
 # available. This is darwin specific since it's currently only needed on darwin.
 
 
 def get_asan_rtlib():
     if not 'Address' in config.llvm_use_sanitizer or \
        not 'Darwin' in config.host_os or \
        not 'x86' in config.host_triple: