[demangler] PPC and S390: Fix parsing of e-prefixed long double literals

Summary:
This patch is to fix the parsing of long double literals encoded with the e prefix on PowerPC and S390. For both PowerPC and S390, type code e is used for 64-bit long double literals and g is used for 128-bit long double literals. libcxxabi test case test_demangle.pass.cpp fails without the fix.

Authored by: xingxue-ibm

Reviewers: hubert.reinterpretcast, jasonliu, erik.pilkington, uweigand, mclow.li
sts, libc++abi

Reviewed by: hubert.reinterpretcast, erik.pilkington

Differential Revision: https://reviews.llvm.org/D74163

Author: xingxue-ibm

libcxxabi/src/demangle/ItaniumDemangle.h

@@ -4225,7 +4225,13 @@ Node *AbstractManglingParser<Derived, Alloc>::parseExprPrimary() {
     return getDerived().template parseFloatingLiteral<double>();
   case 'e':
     ++First;
+#if defined(__powerpc__) || defined(__s390__)
+    // Handle cases where long doubles encoded with e have the same size
+    // and representation as doubles.
+    return getDerived().template parseFloatingLiteral<double>();
+#else
     return getDerived().template parseFloatingLiteral<long double>();
+#endif
   case '_':
     if (consumeIf("_Z")) {
       Node *R = getDerived().parseEncoding();

llvm/include/llvm/Demangle/ItaniumDemangle.h

@@ -4225,7 +4225,13 @@ Node *AbstractManglingParser<Derived, Alloc>::parseExprPrimary() {
     return getDerived().template parseFloatingLiteral<double>();
   case 'e':
     ++First;
+#if defined(__powerpc__) || defined(__s390__)
+    // Handle cases where long doubles encoded with e have the same size
+    // and representation as doubles.
+    return getDerived().template parseFloatingLiteral<double>();
+#else
     return getDerived().template parseFloatingLiteral<long double>();
+#endif
   case '_':
     if (consumeIf("_Z")) {
       Node *R = getDerived().parseEncoding();