Enable cross compilation for cpython 2.7 (#50245)

pkgs/development/interpreters/python/cpython/2.7/cross-compile.patch

@@ -0,0 +1,32 @@
+--- ./setup.py.orig	2018-04-29 15:47:33.000000000 -0700
++++ ./setup.py	2018-11-11 09:41:58.097682221 -0800
+@@ -458,8 +458,6 @@
+         if not cross_compiling:
+             add_dir_to_list(self.compiler.library_dirs, '/usr/local/lib')
+             add_dir_to_list(self.compiler.include_dirs, '/usr/local/include')
+-        if cross_compiling:
+-            self.add_gcc_paths()
+         self.add_multiarch_paths()
+ 
+         # Add paths specified in the environment variables LDFLAGS and
+@@ -517,7 +515,10 @@
+         # be assumed that no additional -I,-L directives are needed.
+         inc_dirs = self.compiler.include_dirs[:]
+         lib_dirs = self.compiler.library_dirs[:]
+-        if not cross_compiling:
++        if cross_compiling:
++            inc_dirs = []
++            lib_dirs = []
++        else:
+             for d in (
+                 '/usr/include',
+                 ):
+@@ -582,6 +584,8 @@ class PyBuildExt(build_ext):
+         # Some modules that are normally always on:
+         #exts.append( Extension('_weakref', ['_weakref.c']) )
+ 
++        self.compiler.library_dirs = lib_dirs + [ '.' ]
++
+         # array objects
+         exts.append( Extension('array', ['arraymodule.c']) )
+ 

pkgs/development/interpreters/python/cpython/2.7/default.nix

@@ -104,6 +104,8 @@ let
       # only works for GCC and Apple Clang. This makes distutils to call C++
       # compiler when needed.
       ./python-2.7-distutils-C++.patch
+    ] ++ optional (stdenv.hostPlatform != stdenv.buildPlatform) [
+      ./cross-compile.patch
     ];
 
   preConfigure = ''
@@ -176,10 +178,14 @@ let
     LIBRARY_PATH = makeLibraryPath paths;
   };
 
+  # Python 2.7 needs this
+  crossCompileEnv = stdenv.lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform)
+                      { _PYTHON_HOST_PLATFORM = stdenv.hostPlatform.config; };
+
   # Build the basic Python interpreter without modules that have
   # external dependencies.
 
-in stdenv.mkDerivation {
+in stdenv.mkDerivation ({
     name = "python-${version}";
     pythonVersion = majorVersion;
 
@@ -278,4 +284,4 @@ in stdenv.mkDerivation {
       # in case both 2 and 3 are installed.
       priority = -100;
     };
-  }
+  } // crossCompileEnv)