Append to, rather than replace, existing RUSTFLAGS when building (#103)

Author: ahesford

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Respect `PYO3_PYTHON` and `PYTHON_SYS_EXECUTABLE` environment variables if set. [#96](https://github.com/PyO3/setuptools-rust/pull/96)
 - Add runtime dependency on setuptools >= 46.1. [#102](https://github.com/PyO3/setuptools-rust/pull/102)
+- Append to, rather than replace, existing RUSTFLAGS when building. [#103](https://github.com/PyO3/setuptools-rust/pull/103)
 
 ## 0.11.6 (2020-12-13)
 

setuptools_rust/build.py

@@ -186,7 +186,7 @@ def build_extension(self, ext):
             rustflags += " -C target-cpu=native"
 
         if rustflags:
-            env["RUSTFLAGS"] = rustflags
+            env["RUSTFLAGS"] = (env.get("RUSTFLAGS", "") + " " + rustflags).strip()
 
         # Execute cargo
         try: