Add cold attribute to one time construction APIs

[Aditya K]

Revised patch with _GLIBCXX_COLD added at the end.

```
commit 3dc9f9a8461b1c88e991ceb517e5fdd81f268d1e
Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
Date:   Thu Aug 13 09:41:34 2020 -0700

    Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose,
    namely guarding local static variable initialization,
    and since that purpose is definitionally cold, it should be attributed as cold.
    Similarly for __cxa_guard_release and __cxa_guard_abort

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4..f6f954eef 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -35,20 +35,21 @@
 
 // The datestamp of the C++ library in compressed ISO date format.
 #define __GLIBCXX__
 
 // Macros for various attributes.
 //   _GLIBCXX_PURE
 //   _GLIBCXX_CONST
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
+//   _GLIBCXX_COLD
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
 
 #ifndef _GLIBCXX_CONST
 # define _GLIBCXX_CONST __attribute__ ((__const__))
 #endif
 
 #ifndef _GLIBCXX_NORETURN
 # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
@@ -67,20 +68,24 @@
 #define _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
 
 #if _GLIBCXX_HAVE_ATTRIBUTE_VISIBILITY
 # define _GLIBCXX_VISIBILITY(V) __attribute__ ((__visibility__ (#V)))
 #else
 // If this is not supplied by the OS-specific or CPU-specific
 // headers included below, it will be defined to an empty default.
 # define _GLIBCXX_VISIBILITY(V) _GLIBCXX_PSEUDO_VISIBILITY(V)
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((cold))
+#endif
+
 // Macros for deprecated attributes.
 //   _GLIBCXX_USE_DEPRECATED
 //   _GLIBCXX_DEPRECATED
 //   _GLIBCXX17_DEPRECATED
 //   _GLIBCXX20_DEPRECATED( string-literal )
 #ifndef _GLIBCXX_USE_DEPRECATED
 # define _GLIBCXX_USE_DEPRECATED 1
 #endif
 
 #if defined(__DEPRECATED) && (__cplusplus >= 201103L)
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecd..24c1366e2 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -108,27 +108,27 @@ namespace __cxxabiv1
   __cxa_vec_delete2(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*));
 
   void
   __cxa_vec_delete3(void* __array_address, size_t __element_size,
 		    size_t __padding_size, __cxa_cdtor_type __destructor,
 		    void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int
   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
 
   void
   __cxa_finalize(void*);
 
   // TLS destruction.
   int
```

From: Aditya K
Sent: Thursday, August 13, 2020 10:47 AM
To: Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org>; jwakely.gcc@gmail.com <jwakely.gcc@gmail.com>
Subject: Add cold attribute to one time construction APIs 
 
This would help compiler optimize local static objects.

```
commit e2f299679ddf56a6d6d71ea9d589cd76b2ca107b
Author: Aditya Kumar <1894981+hiraditya@users.noreply.github.com>
Date:   Thu Aug 13 09:41:34 2020 -0700

    Add cold attribute to one time construction APIs
    
    __cxa_guard_acquire is used for only one purpose,
    namely guarding local static variable initialization,
    and since that purpose is definitionally cold, it should be attributed as cold.
    Similarly for __cxa_guard_release and __cxa_guard_abort

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index b1fad59d4..359e955a7 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -39,20 +39,24 @@
 // Macros for various attributes.
 //   _GLIBCXX_PURE
 //   _GLIBCXX_CONST
 //   _GLIBCXX_NORETURN
 //   _GLIBCXX_NOTHROW
 //   _GLIBCXX_VISIBILITY
 #ifndef _GLIBCXX_PURE
 # define _GLIBCXX_PURE __attribute__ ((__pure__))
 #endif
 
+#ifndef _GLIBCXX_COLD
+# define _GLIBCXX_COLD __attribute__ ((cold))
+#endif
+
 #ifndef _GLIBCXX_CONST
 # define _GLIBCXX_CONST __attribute__ ((__const__))
 #endif
 
 #ifndef _GLIBCXX_NORETURN
 # define _GLIBCXX_NORETURN __attribute__ ((__noreturn__))
 #endif
 
 // See below for C++
 #ifndef _GLIBCXX_NOTHROW
diff --git a/libstdc++-v3/libsupc++/cxxabi.h b/libstdc++-v3/libsupc++/cxxabi.h
index 000713ecd..24c1366e2 100644
--- a/libstdc++-v3/libsupc++/cxxabi.h
+++ b/libstdc++-v3/libsupc++/cxxabi.h
@@ -108,27 +108,27 @@ namespace __cxxabiv1
   __cxa_vec_delete2(void* __array_address, size_t __element_size,
                     size_t __padding_size, __cxa_cdtor_type __destructor,
                     void (*__dealloc) (void*));
 
   void
   __cxa_vec_delete3(void* __array_address, size_t __element_size,
                     size_t __padding_size, __cxa_cdtor_type __destructor,
                     void (*__dealloc) (void*, size_t));
 
   int
-  __cxa_guard_acquire(__guard*);
+  __cxa_guard_acquire(__guard*) _GLIBCXX_COLD;
 
   void
-  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   void
-  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
+  __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW _GLIBCXX_COLD;
 
   // DSO destruction.
   int
   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
 
   void
   __cxa_finalize(void*);
 
   // TLS destruction.
   int
```