Fix a couple C++ build issues

Building mingw GDB with --enable-build-with-cxx shows:

../../binutils-gdb/gdb/python/py-unwind.c:500:45: error: cannot convert 'cached_frame_info::reg_info*' to 'pyuw_prev_register(frame_info*, void**, int)::reg_info*' in initialization
   struct reg_info *reg_info = cached_frame->reg;
                                             ^
../../binutils-gdb/gdb/python/py-unwind.c:501:60: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
   struct reg_info *reg_info_end = reg_info + cached_frame->reg_count;
                                                            ^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
   struct reg_info *reg_info = cached_frame->reg;
          ^
../../binutils-gdb/gdb/python/py-unwind.c:505:37: error: cannot increment a pointer to incomplete type 'pyuw_prev_register(frame_info*, void**, int)::reg_info'
   for (; reg_info < reg_info_end; ++reg_info)
                                     ^
../../binutils-gdb/gdb/python/py-unwind.c:507:29: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
       if (regnum == reg_info->number)
                             ^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
   struct reg_info *reg_info = cached_frame->reg;
          ^
../../binutils-gdb/gdb/python/py-unwind.c:508:68: error: invalid use of incomplete type 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
         return frame_unwind_got_bytes (this_frame, regnum, reg_info->data);
                                                                    ^
../../binutils-gdb/gdb/python/py-unwind.c:500:10: error: forward declaration of 'struct pyuw_prev_register(frame_info*, void**, int)::reg_info'
   struct reg_info *reg_info = cached_frame->reg;
          ^
../../binutils-gdb/gdb/python/py-unwind.c: In function 'int pyuw_sniffer(const frame_unwind*, frame_info*, void**)':
../../binutils-gdb/gdb/python/py-unwind.c:574:70: warning: invalid conversion from 'void*' to 'cached_frame_info*' [-fpermissive]
                             reg_count * sizeof (cached_frame->reg[0]));
                                                                      ^
../../binutils-gdb/gdb/python/py-unwind.c: In function 'void pyuw_on_new_gdbarch(gdbarch*)':
../../binutils-gdb/gdb/python/py-unwind.c:636:47: warning: invalid conversion from 'void*' to 'pyuw_gdbarch_data_type*' [-fpermissive]
       gdbarch_data (newarch, pyuw_gdbarch_data);
                                               ^
../../binutils-gdb/gdb/python/py-unwind.c:647:29: warning: invalid conversion from 'void*' to 'const frame_data*' [-fpermissive]
       unwinder->unwind_data = (void *) newarch;
                             ^
../../binutils-gdb/gdb/python/py-unwind.c: At global scope:
../../binutils-gdb/gdb/python/py-unwind.c:699:21: error: redefinition of 'PyTypeObject pending_frame_object_type'
 static PyTypeObject pending_frame_object_type =
                     ^
../../binutils-gdb/gdb/python/py-unwind.c:96:21: error: 'PyTypeObject pending_frame_object_type' previously declared here
 static PyTypeObject pending_frame_object_type
                     ^
../../binutils-gdb/gdb/python/py-unwind.c:749:21: error: redefinition of 'PyTypeObject unwind_info_object_type'
 static PyTypeObject unwind_info_object_type =
                     ^
../../binutils-gdb/gdb/python/py-unwind.c:99:21: error: 'PyTypeObject unwind_info_object_type' previously declared here
 static PyTypeObject unwind_info_object_type
                     ^

The first kind of error is caused by the embedded struct definition,
so move it out of the parent struct.

The second kind of error is caused by forward declaring a static
global variable, which works in C, but not in C++ (or C with
-fno-common).  Make it using extern instead, like done in other
similar cases.

gdb/ChangeLog:
2015-05-15  Yuanhui Zhang  <asmwarrior@gmail.com>

	* python/py-unwind.c (struct reg_info): Move out of ...
	(struct cached_frame_info): ... this scope.
	(pending_frame_object_type, unwind_info_object_type): Make extern.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2015-05-15  Yuanhui Zhang  <asmwarrior@gmail.com>
+
+	* python/py-unwind.c (struct reg_info): Move out of ...
+	(struct cached_frame_info): ... this scope.
+	(pending_frame_object_type, unwind_info_object_type): Make extern.
+
 2015-05-15  Joel Brobecker  <brobecker@adacore.com>
 
 	* ada-lang.c (ada_value_primitive_packed_val): Make sure

gdb/python/py-unwind.c

@@ -72,6 +72,15 @@ typedef struct
 /* The data we keep for a frame we can unwind: frame ID and an array of
    (register_number, register_value) pairs.  */
 
+struct reg_info
+{
+  /* Register number.  */
+  int number;
+
+  /* Register data bytes pointer.  */
+  gdb_byte data[MAX_REGISTER_SIZE];
+};
+
 typedef struct
 {
   /* Frame ID.  */
@@ -83,20 +92,13 @@ typedef struct
   /* Length of the `reg' array below.  */
   int reg_count;
 
-  struct reg_info
+  struct reg_info reg[];
-  {
-    /* Register number.  */
-    int number;
-
-    /* Register data bytes pointer.  */
-    gdb_byte data[MAX_REGISTER_SIZE];
-  } reg[];
 } cached_frame_info;
 
-static PyTypeObject pending_frame_object_type
+extern PyTypeObject pending_frame_object_type
     CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("pending_frame_object");
 
-static PyTypeObject unwind_info_object_type
+extern PyTypeObject unwind_info_object_type
     CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("unwind_info_object");
 
 static unsigned int pyuw_debug = 0;
@@ -696,7 +698,7 @@ static PyMethodDef pending_frame_object_methods[] =
   {NULL}  /* Sentinel */
 };
 
-static PyTypeObject pending_frame_object_type =
+PyTypeObject pending_frame_object_type =
 {
   PyVarObject_HEAD_INIT (NULL, 0)
   "gdb.PendingFrame",             /* tp_name */
@@ -746,7 +748,7 @@ static PyMethodDef unwind_info_object_methods[] =
   { NULL }  /* Sentinel */
 };
 
-static PyTypeObject unwind_info_object_type =
+PyTypeObject unwind_info_object_type =
 {
   PyVarObject_HEAD_INIT (NULL, 0)
   "gdb.UnwindInfo",               /* tp_name */