Fix for temp file on windows

On windows the temp file cannot be opened a second time while
it is still opened by python. Close the file in python before
asking the compiler to read it.

See https://docs.python.org/3.7/library/tempfile.html#tempfile.NamedTemporaryFile

Author: isuruf

setup.py

@@ -42,12 +42,13 @@ def has_flag(compiler, flagname):
     the specified compiler.
     """
     import tempfile
-    with tempfile.NamedTemporaryFile('w', suffix='.cpp') as f:
+    with tempfile.NamedTemporaryFile('w', suffix='.cpp', delete=False) as f:
         f.write('int main (int argc, char **argv) { return 0; }')
-        try:
-            compiler.compile([f.name], extra_postargs=[flagname])
-        except setuptools.distutils.errors.CompileError:
-            return False
+        fname = f.name
+    try:
+        compiler.compile([fname], extra_postargs=[flagname])
+    except setuptools.distutils.errors.CompileError:
+        return False
     return True