Fix #20894 (#20895)

- pragma(msg) interprets printf format specifiers

compiler/src/dmd/pragmasem.d

@@ -568,7 +568,7 @@ private bool pragmaMsgSemantic(Loc loc, Scope* sc, Expressions* args)
     else
     {
         buf.writestring("\n");
-        fprintf(stderr, buf.extractChars);
+        fprintf(stderr, "%s", buf.extractChars);
     }
     return true;
 }

compiler/test/compilable/bug11735.d

@@ -13,6 +13,7 @@ print dstring
 foo_str
 foo_wstr
 foo_dstr
+X%nY
 ---
 */
 
@@ -33,4 +34,7 @@ void main()
     pragma(msg, a);
     pragma(msg, b);
     pragma(msg, c);
+
+    // https://github.com/dlang/dmd/issues/20894
+    pragma(msg, "X%nY");
 }