[regexp] Port RegExpExecStub to CSA (mostly)

src/s390/interface-descriptors-s390.cc

Index: src/s390/interface-descriptors-s390.cc
diff --git a/src/s390/interface-descriptors-s390.cc b/src/s390/interface-descriptors-s390.cc
index 8060cfe94282e2696f0ee7455a3e5b7b48cccc8d..83c08782d60725fee3abdcb0159fb9bf63b3e363 100644
--- a/src/s390/interface-descriptors-s390.cc
+++ b/src/s390/interface-descriptors-s390.cc
@@ -56,6 +56,12 @@ const Register MathPowIntegerDescriptor::exponent() {
   return MathPowTaggedDescriptor::exponent();
 }
 
+const Register RegExpExecDescriptor::StringRegister() { return r2; }
+const Register RegExpExecDescriptor::LastIndexRegister() { return r3; }
+const Register RegExpExecDescriptor::StringStartRegister() { return r4; }
+const Register RegExpExecDescriptor::StringEndRegister() { return r5; }
+const Register RegExpExecDescriptor::CodeRegister() { return r9; }
+
 const Register GrowArrayElementsDescriptor::ObjectRegister() { return r2; }
 const Register GrowArrayElementsDescriptor::KeyRegister() { return r5; }