Change __cpp_explicit_bool to __cpp_conditional_explicit.

People objected to the old macro name as unclear, so it was changed.

	* c-cppbuiltin.c (c_cpp_builtins): Change __cpp_explicit_bool to
	__cpp_conditional_explicit.

From-SVN: r266050

gcc/c-family/ChangeLog

+2018-11-12  Jason Merrill  <jason@redhat.com>
+
+	* c-cppbuiltin.c (c_cpp_builtins): Change __cpp_explicit_bool to
+	__cpp_conditional_explicit.
+
 2018-11-09  Martin Sebor  <msebor@redhat.com>
 
 	PR middle-end/81824

gcc/c-family/c-cppbuiltin.c

@@ -978,7 +978,7 @@ c_cpp_builtins (cpp_reader *pfile)
       if (cxx_dialect > cxx17)
 	{
 	  /* Set feature test macros for C++2a.  */
-	  cpp_define (pfile, "__cpp_explicit_bool=201806");
+	  cpp_define (pfile, "__cpp_conditional_explicit=201806");
 	  cpp_define (pfile, "__cpp_nontype_template_parameter_class=201806");
 	}
       if (flag_concepts)

gcc/testsuite/g++.dg/cpp2a/feat-cxx2a.C

@@ -418,6 +418,10 @@
 
 // C++20 features
 
+#if __cpp_conditional_explicit != 201806
+# error "__cpp_conditional_explicit != 201806"
+#endif
+
 #if __cpp_nontype_template_parameter_class != 201806
 # error "__cpp_nontype_template_parameter_class != 201806"
 #endif