Toolchains: Update to GCC 10.5.0

All toolchain dependencies are circa the GCC 10.5.0 release:

  GCC 10.5.0, binutils 2.40, gmp 6.2.1, mpfr 4.1.1, mpc 1.3.1, isl 0.24

Native:

 * arm - mini2g, nano2g works
       - ipod6g hangs at logo display
 * mips - xduoox3 works
 * m68k - binaries untested

Hosted:

 * arm - samsungypr0 works
 * mips - xduoox3ii works
 * Android NDK - unchanged at GCC 4.9.4

Change-Id: Ic157255d76030e66325719e64331f553cb7c4363

tools/toolchain-patches/gcc-libcpp17.patch

@@ -0,0 +1,66 @@
+diff --git a/gcc/system.h b/gcc/system.h
+index d04f8fd33..636084682 100644
+--- a/gcc/system.h
++++ b/gcc/system.h
+@@ -197,25 +197,6 @@ extern int fprintf_unlocked (FILE *, const char *, ...);
+ /* Include <string> before "safe-ctype.h" to avoid GCC poisoning
+    the ctype macros through safe-ctype.h */
+ 
+-#ifdef __cplusplus
+-#ifdef INCLUDE_STRING
+-# include <string>
+-#endif
+-#endif
+-
+-/* There are an extraordinary number of issues with <ctype.h>.
+-   The last straw is that it varies with the locale.  Use libiberty's
+-   replacement instead.  */
+-#include "safe-ctype.h"
+-
+-#include <sys/types.h>
+-
+-#include <errno.h>
+-
+-#if !defined (errno) && defined (HAVE_DECL_ERRNO) && !HAVE_DECL_ERRNO
+-extern int errno;
+-#endif
+-
+ #ifdef __cplusplus
+ #if defined (INCLUDE_ALGORITHM) || !defined (HAVE_SWAP_IN_UTILITY)
+ # include <algorithm>
+@@ -229,6 +210,9 @@ extern int errno;
+ #ifdef INCLUDE_SET
+ # include <set>
+ #endif
++#ifdef INCLUDE_STRING
++# include <string>
++#endif
+ #ifdef INCLUDE_VECTOR
+ # include <vector>
+ #endif
+@@ -237,6 +221,25 @@ extern int errno;
+ # include <utility>
+ #endif
+ 
++#ifdef __cplusplus
++#ifdef INCLUDE_STRING
++# include <string>
++#endif
++#endif
++
++/* There are an extraordinary number of issues with <ctype.h>.
++   The last straw is that it varies with the locale.  Use libiberty's
++   replacement instead.  */
++#include "safe-ctype.h"
++
++#include <sys/types.h>
++
++#include <errno.h>
++
++#if !defined (errno) && defined (HAVE_DECL_ERRNO) && !HAVE_DECL_ERRNO
++extern int errno;
++#endif
++
+ /* Some of glibc's string inlines cause warnings.  Plus we'd rather
+    rely on (and therefore test) GCC's string builtins.  */
+ #define __NO_STRING_INLINES