fix(profiling): don't build _memalloc extension when using Pyston (backport #3566) (#3592)

This is an automatic backport of pull request #3566 done by [Mergify](https://mergify.com).


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Author: mergify[bot]

docs/spelling_wordlist.txt

@@ -120,6 +120,7 @@ pymongo
 pymysql
 pynamodb
 pyodbc
+pyston
 pytest
 quickstart
 redis

releasenotes/notes/fix-pyston-memalloc-e8f4002e5c11df8c.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fix issue building ``ddtrace`` for the Pyston Python implementation by
+    not building the ``_memalloc`` extension anymore when using Pyston. 

setup.py

@@ -16,6 +16,8 @@
 
 DEBUG_COMPILE = "DD_COMPILE_DEBUG" in os.environ
 
+IS_PYSTON = hasattr(sys, "pyston_version_info")
+
 
 def load_module_from_project_file(mod_name, fname):
     """
@@ -184,7 +186,7 @@ def get_exts_for(name):
         ddwaf_libraries = ["ddwaf"]
 
 
-if sys.version_info[:2] >= (3, 4):
+if sys.version_info[:2] >= (3, 4) and not IS_PYSTON:
     ext_modules = [
         Extension(
             "ddtrace.profiling.collector._memalloc",