[Ada] Improve doc on Warning_As_Error

2019-09-18  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* doc/gnat_rm/implementation_defined_pragmas.rst: Improve doc on
	Warning_As_Error.
	* gnat_rm.texi: Regenerate.

From-SVN: r275842

gcc/ada/ChangeLog

 2019-09-18  Arnaud Charlet  <charlet@adacore.com>
 
+	* doc/gnat_rm/implementation_defined_pragmas.rst: Improve doc on
+	Warning_As_Error.
+	* gnat_rm.texi: Regenerate.
+
+2019-09-18  Arnaud Charlet  <charlet@adacore.com>
+
 	* doc/gnat_rm/implementation_defined_characteristics.rst,
 	doc/gnat_rm/implementation_defined_pragmas.rst,
 	doc/gnat_rm/implementation_of_specific_ada_features.rst: Remove

gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst

@@ -7489,9 +7489,11 @@ message string (it is not necessary to put an asterisk at the start and
 the end of the message, since this is implied).
 
 Another possibility for the static_string_EXPRESSION which works whether
-or not error tags are enabled (*-gnatw.d*) is to use the
+or not error tags are enabled (*-gnatw.d*) is to use a single
 *-gnatw* tag string, enclosed in brackets,
-as shown in the example below, to treat a class of warnings as errors.
+as shown in the example below, to treat one category of warnings as errors.
+Note that if you want to treat multiple categories of warnings as errors,
+you can use multiple pragma Warning_As_Error.
 
 The above use of patterns to match the message applies only to warning
 messages generated by the front end. This pragma can also be applied to

gcc/ada/gnat_rm.texi

@@ -8994,9 +8994,11 @@ message string (it is not necessary to put an asterisk at the start and
 the end of the message, since this is implied).
 
 Another possibility for the static_string_EXPRESSION which works whether
-or not error tags are enabled (@emph{-gnatw.d}) is to use the
+or not error tags are enabled (@emph{-gnatw.d}) is to use a single
 @emph{-gnatw} tag string, enclosed in brackets,
-as shown in the example below, to treat a class of warnings as errors.
+as shown in the example below, to treat one category of warnings as errors.
+Note that if you want to treat multiple categories of warnings as errors,
+you can use multiple pragma Warning_As_Error.
 
 The above use of patterns to match the message applies only to warning
 messages generated by the front end. This pragma can also be applied to