libstdc++: Add inline to maybe-constexpr functions (PR 92927)

Originally these functions were always inline. I changed them in r277342
to be always constexpr, then in r277588 changed them to be constexpr for
C++14, but I didn't restore the 'inline' for C++11. That leads to linker
errors when libstdc++.so is built unoptimized, because those functions
don't get instantiated in src/c++11/string-inst.o

	PR libstdc++/92927
	* include/bits/alloc_traits.h (__alloc_on_copy, __alloc_on_move)
	(__alloc_on_swap): Add inline specifier.

From-SVN: r279656

libstdc++-v3/ChangeLog

+2019-12-20  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/92927
+	* include/bits/alloc_traits.h (__alloc_on_copy, __alloc_on_move)
+	(__alloc_on_swap): Add inline specifier.
+
 2019-12-20  Jerome Lambourg  <lambourg@adacore.com>
 
 	* acinclude.m4 (GLIBCXX_CHECK_SETRLIMIT): Test with AC_LANG_CPLUSPLUS.

libstdc++-v3/include/bits/alloc_traits.h

@@ -567,7 +567,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _Alloc>
-    _GLIBCXX14_CONSTEXPR void
+    _GLIBCXX14_CONSTEXPR inline void
     __alloc_on_copy(_Alloc& __one, const _Alloc& __two)
     {
       typedef allocator_traits<_Alloc> __traits;
@@ -599,7 +599,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _Alloc>
-    _GLIBCXX14_CONSTEXPR void
+    _GLIBCXX14_CONSTEXPR inline void
     __alloc_on_move(_Alloc& __one, _Alloc& __two)
     {
       typedef allocator_traits<_Alloc> __traits;
@@ -626,7 +626,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _Alloc>
-    _GLIBCXX14_CONSTEXPR void
+    _GLIBCXX14_CONSTEXPR inline void
     __alloc_on_swap(_Alloc& __one, _Alloc& __two)
     {
       typedef allocator_traits<_Alloc> __traits;