Issue #7117: Backport missing pystrtod.h declarations from py3k.

Include/pystrtod.h

@@ -12,6 +12,9 @@ PyAPI_FUNC(double) PyOS_ascii_atof(const char *str);
 /* Deprecated in 2.7 and 3.1. Will disappear in 2.8 (if it exists) and 3.2 */
 PyAPI_FUNC(char *) PyOS_ascii_formatd(char *buffer, size_t buf_len,
                                       const char *format, double d);
+PyAPI_FUNC(double) PyOS_string_to_double(const char *str,
+                                         char **endptr,
+                                         PyObject *overflow_exception);
 
 /* The caller is responsible for calling PyMem_Free to free the buffer
    that's is returned. */
@@ -21,6 +24,8 @@ PyAPI_FUNC(char *) PyOS_double_to_string(double val,
                                          int flags,
                                          int *type);
 
+PyAPI_FUNC(double) _Py_parse_inf_or_nan(const char *p, char **endptr);
+
 
 /* PyOS_double_to_string's "flags" parameter can be set to 0 or more of: */
 #define Py_DTSF_SIGN      0x01 /* always add the sign */