PYTHON-3760 Add C extension building as part of tox test environment (#1255)

Author: blink1073

setup.py

@@ -126,6 +126,8 @@ def run(self):
         try:
             build_ext.run(self)
         except Exception:
+            if "TOX_ENV_NAME" in os.environ:
+                raise
             e = sys.exc_info()[1]
             sys.stdout.write("%s\n" % str(e))
             warnings.warn(
@@ -141,6 +143,8 @@ def build_extension(self, ext):
         try:
             build_ext.build_extension(self, ext)
         except Exception:
+            if "TOX_ENV_NAME" in os.environ:
+                raise
             e = sys.exc_info()[1]
             sys.stdout.write("%s\n" % str(e))
             warnings.warn(