[2.7] bpo-37329: valgrind: ignore _PyWarnings_Init false alarms (GH-14202)

_PyWarnings_Init() only allocates memory once at startup but it is
not released at exit. Ignore this issue to be able to catch other
bugs more easily.

Misc/NEWS.d/next/Core and Builtins/2019-06-18-15-08-32.bpo-37329.7XVDRv.rst

+valgrind: suppress a false alarm in memory leak checks. _PyWarnings_Init()
+only allocates memory once at startup but it is not released at exit. Ignore
+this issue to be able to catch other bugs more easily.

Misc/valgrind-python.supp

@@ -103,6 +103,14 @@
    fun:COMMENT_THIS_LINE_TO_DISABLE_LEAK_WARNING
 }
 
+{
+   bpo-37329: _PyWarnings_Init allocates memory at startup, but doesn't release it at exit
+   Memcheck:Leak
+   fun:malloc
+   ...
+   fun:_PyWarnings_Init
+}
+
 #
 # Non-python specific leaks
 #