From 923852857d561a1b21580076b2670d22dcbdf984 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Mon, 30 Sep 2013 22:13:17 +0200
Subject: [PATCH] Issue #12641: Avoid passing "-mno-cygwin" to the mingw32
 compiler, except when necessary. Patch by Oscar Benjamin.

---
 Lib/distutils/cygwinccompiler.py | 28 +++++++++++++++++++++-------
 Misc/ACKS                        |  1 +
 Misc/NEWS                        |  3 +++
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/Lib/distutils/cygwinccompiler.py b/Lib/distutils/cygwinccompiler.py
index a1ee815c6c..5d116876a3 100644
--- a/Lib/distutils/cygwinccompiler.py
+++ b/Lib/distutils/cygwinccompiler.py
@@ -319,13 +319,18 @@ class Mingw32CCompiler (CygwinCCompiler):
         else:
             entry_point = ''
 
-        self.set_executables(compiler='gcc -mno-cygwin -O -Wall',
-                             compiler_so='gcc -mno-cygwin -mdll -O -Wall',
-                             compiler_cxx='g++ -mno-cygwin -O -Wall',
-                             linker_exe='gcc -mno-cygwin',
-                             linker_so='%s -mno-cygwin %s %s'
-                                        % (self.linker_dll, shared_option,
-                                           entry_point))
+        if self.gcc_version < '4' or is_cygwingcc():
+            no_cygwin = ' -mno-cygwin'
+        else:
+            no_cygwin = ''
+
+        self.set_executables(compiler='gcc%s -O -Wall' % no_cygwin,
+                             compiler_so='gcc%s -mdll -O -Wall' % no_cygwin,
+                             compiler_cxx='g++%s -O -Wall' % no_cygwin,
+                             linker_exe='gcc%s' % no_cygwin,
+                             linker_so='%s%s %s %s'
+                                    % (self.linker_dll, no_cygwin,
+                                       shared_option, entry_point))
         # Maybe we should also append -mthreads, but then the finished
         # dlls need another dll (mingwm10.dll see Mingw32 docs)
         # (-mthreads: Support thread-safe exception handling on `Mingw32')
@@ -447,3 +452,12 @@ def get_versions():
     else:
         dllwrap_version = None
     return (gcc_version, ld_version, dllwrap_version)
+
+def is_cygwingcc():
+    '''Try to determine if the gcc that would be used is from cygwin.'''
+    out = os.popen('gcc -dumpmachine', 'r')
+    out_string = out.read()
+    out.close()
+    # out_string is the target triplet cpu-vendor-os
+    # Cygwin's gcc sets the os to 'cygwin'
+    return out_string.strip().endswith('cygwin')
diff --git a/Misc/ACKS b/Misc/ACKS
index 6048ed8dd7..cbef1f00fc 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -84,6 +84,7 @@ Ben Bell
 Thomas Bellman
 Alexander “Саша” Belopolsky
 David Benjamin
+Oscar Benjamin
 Andrew Bennetts
 Andy Bensky
 Bennett Benson
diff --git a/Misc/NEWS b/Misc/NEWS
index af6ed7e96c..54753cd923 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -32,6 +32,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12641: Avoid passing "-mno-cygwin" to the mingw32 compiler, except
+  when necessary.  Patch by Oscar Benjamin.
+
 - Properly initialize all fields of a SSL object after allocation.
 
 - Issue #4366: Fix building extensions on all platforms when --enable-shared
-- 
2.50.1