add patch for gcc@8 for python 2.7.14 (#8990)

* add gcc8 patch for python 2.7.14

Change-Id: I48cb5e717577d8158d1f7f1fe270156a01940d8a

* add explaining comment

Change-Id: Ia46168e2269d7de47d7ec8d0bf9e3b7696ea8e31

* remove unnecessary part of the patch

Change-Id: Iee763effe2439f0f160c1547640eca4bb9451a68

var/spack/repos/builtin/packages/python/gcc-8-2.7.14.patch

@@ -0,0 +1,35 @@
+diff --git a/Include/objimpl.h b/Include/objimpl.h
+index 5f2868332955..cbf6bc3f8763 100644
+--- a/Include/objimpl.h
++++ b/Include/objimpl.h
+@@ -248,6 +248,20 @@ PyAPI_FUNC(PyVarObject *) _PyObject_GC_Resize(PyVarObject *, Py_ssize_t);
+ /* for source compatibility with 2.2 */
+ #define _PyObject_GC_Del PyObject_GC_Del
+ 
++/*
++ * Former over-aligned definition of PyGC_Head, used to compute the size of the
++ * padding for the new version below.
++ */
++union _gc_head;
++union _gc_head_old {
++    struct {
++        union _gc_head_old *gc_next;
++        union _gc_head_old *gc_prev;
++        Py_ssize_t gc_refs;
++    } gc;
++    long double dummy;
++};
++
+ /* GC information is stored BEFORE the object structure. */
+ typedef union _gc_head {
+     struct {
+@@ -255,7 +269,8 @@ typedef union _gc_head {
+         union _gc_head *gc_prev;
+         Py_ssize_t gc_refs;
+     } gc;
+-    long double dummy;  /* force worst-case alignment */
++    double dummy; /* Force at least 8-byte alignment. */
++    char dummy_padding[sizeof(union _gc_head_old)];
+ } PyGC_Head;
+ 
+ extern PyGC_Head *_PyGC_generation0;

var/spack/repos/builtin/packages/python/package.py

@@ -118,6 +118,10 @@ class Python(AutotoolsPackage):
     patch('cray-rpath-2.3.patch', when="@2.3:3.0.1 platform=cray")
     patch('cray-rpath-3.1.patch', when="@3.1:3.99  platform=cray")
 
+    # Fixes an alignment problem with more aggressive optimization in gcc8
+    # https://github.com/python/cpython/commit/0b91f8a668201fc58fa732b8acc496caedfdbae0
+    patch('gcc-8-2.7.14.patch', when="@2.7.14 %gcc@8:")
+
     # For more information refer to this bug report:
     # https://bugs.python.org/issue29712
     conflicts(