[spec] Allow multiple message arguments for static assert

Counterpart for:
dlang/dmd#14611

Author: ntrel

spec/version.dd

@@ -741,7 +741,7 @@ $(H2 $(LEGACY_LNAME2 StaticAssert, static-assert, Static Assert))
 
 $(GRAMMAR
 $(GNAME StaticAssert):
-    $(D static assert $(LPAREN)) $(GLINK2 expression, AssertArguments) $(D $(RPAREN) ;)
+    $(D static assert $(LPAREN)) $(GLINK2 expression, ArgumentList) $(D $(RPAREN) ;)
 )
 
         $(P The first $(ASSIGNEXPRESSION) is evaluated at compile time, and converted
@@ -750,6 +750,11 @@ $(GNAME StaticAssert):
         and the compile fails.
         )
 
+        $(P On failure, any subsequent $(I AssignExpression)s will each be
+        converted to string and then concatenated. The resulting string will
+        be printed out along with the error diagnostic.
+        )
+
         $(P Unlike $(GLINK2 expression, AssertExpression)s, $(I StaticAssert)s are always
         checked and evaluated by the compiler unless they appear in an
         unsatisfied conditional.
@@ -777,10 +782,6 @@ void foo()
         configurations not supported in the code.
         )
 
-        $(P The optional second $(ASSIGNEXPRESSION) can be used to supply
-        additional information, such as a text string, that will be
-        printed out along with the error diagnostic.
-        )
 $(SPEC_SUBNAV_PREV_NEXT contracts, Contract Programming, traits, Traits)
 )