Add ability to pass flags to rustc

Author: pganssle

setuptools_rust/build.py

@@ -135,6 +135,7 @@ def build_extension(self, ext):
                 args.append("-q")
 
             args.extend(["--", "--crate-type", "cdylib"])
+            args.extend(ext.rustc_flags or [])
 
             # OSX requires special linker argument
             if sys.platform == "darwin":

setuptools_rust/extension.py

@@ -55,6 +55,7 @@ def __init__(
         path,
         args=None,
         features=None,
+        rustc_flags=None,
         rust_version=None,
         quiet=False,
         debug=None,
@@ -73,6 +74,7 @@ def __init__(
         self.name = name
         self.target = target
         self.args = args
+        self.rustc_flags = rustc_flags
         self.binding = binding
         self.rust_version = rust_version
         self.quiet = quiet