Have ZC* imply extensions rather than erroring if not present

disasm/isa_parser.cc

@@ -140,17 +140,22 @@ void isa_parser_t::add_extension(const std::string& ext_str, const char* str)
     if (max_xlen != 32)
       bad_isa_string(str, "'Zcf' requires RV32");
     extension_table['F'] = true;
+    extension_table[EXT_ZCA] = true;
     extension_table[EXT_ZCF] = true;
   } else if (ext_str == "zcb") {
     extension_table[EXT_ZCB] = true;
+    extension_table[EXT_ZCA] = true;
   } else if (ext_str == "zcd") {
     extension_table[EXT_ZCD] = true;
+    extension_table[EXT_ZCA] = true;
     extension_table['F'] = true;
     extension_table['D'] = true;
   } else if (ext_str == "zcmp") {
     extension_table[EXT_ZCMP] = true;
+    extension_table[EXT_ZCA] = true;
   } else if (ext_str == "zcmt") {
     extension_table[EXT_ZCMT] = true;
+    extension_table[EXT_ZCA] = true;
   } else if (ext_str == "zibi") {
     extension_table[EXT_ZIBI] = true;
   } else if (ext_str == "zk") {
@@ -530,11 +535,6 @@ isa_parser_t::isa_parser_t(const char* str, const char *priv)
     bad_isa_string(str, "Zcmp' and 'Zcmt' extensions are incompatible with 'Zcd' extension");
   }
 
-  if ((extension_table[EXT_ZCF] || extension_table[EXT_ZCD] || extension_table[EXT_ZCB] ||
-       extension_table[EXT_ZCMP] || extension_table[EXT_ZCMT]) && !extension_table[EXT_ZCA]) {
-    bad_isa_string(str, "'Zcf/Zcd/Zcb/Zcmp/Zcmt' extensions require 'Zca' extension");
-  }
-
   if (extension_table[EXT_ZACAS] && !extension_table[EXT_ZAAMO]) {
     bad_isa_string(str, "'Zacas' extension requires either the 'A' or the 'Zaamo' extension");
   }