Only include bits/stl_algo.h for C++20.

2018-11-29  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Only include bits/stl_algo.h for C++20.
	* include/std/deque: Only include bits/stl_algo.h for C++20.
	* include/std/string: Ditto.
	* include/std/vector: Ditto.

From-SVN: r266624

libstdc++-v3/ChangeLog

 2018-11-29  Edward Smith-Rowland  <3dw4rd@verizon.net>
 
+	Only include bits/stl_algo.h for C++20.
+	* include/std/deque: Only include bits/stl_algo.h for C++20.
+	* include/std/string: Ditto.
+	* include/std/vector: Ditto.
+
+2018-11-29  Edward Smith-Rowland  <3dw4rd@verizon.net>
+
 	Fix erasure goofs.
 	* include/experimental/deque: Make inline.
 	* include/std/deque: Include bits/stl_algo.h.

libstdc++-v3/include/std/deque

@@ -58,7 +58,9 @@
 #pragma GCC system_header
 
 #include <bits/stl_algobase.h>
-#include <bits/stl_algo.h> // For remove and remove_if
+#if __cplusplus > 201703L
+#  include <bits/stl_algo.h> // For remove and remove_if
+#endif // C++20
 #include <bits/allocator.h>
 #include <bits/stl_construct.h>
 #include <bits/stl_uninitialized.h>

libstdc++-v3/include/std/string

@@ -48,7 +48,9 @@
 #include <bits/stl_function.h> // For less
 #include <ext/numeric_traits.h>
 #include <bits/stl_algobase.h>
-#include <bits/stl_algo.h> // For remove and remove_if
+#if __cplusplus > 201703L
+#  include <bits/stl_algo.h> // For remove and remove_if
+#endif // C++20
 #include <bits/range_access.h>
 #include <bits/basic_string.h>
 #include <bits/basic_string.tcc>

libstdc++-v3/include/std/vector

@@ -58,7 +58,9 @@
 #pragma GCC system_header
 
 #include <bits/stl_algobase.h>
-#include <bits/stl_algo.h> // For remove and remove_if
+#if __cplusplus > 201703L
+#  include <bits/stl_algo.h> // For remove and remove_if
+#endif // C++20
 #include <bits/allocator.h>
 #include <bits/stl_construct.h>
 #include <bits/stl_uninitialized.h>