[flang] Remove GCC 7.2 workarounds (#73574)

The minimum GCC version was bumped from 7.1 to 7.4 so garbage collect
the 7.2 workarounds.

https://reviews.llvm.org/D156286

Author: brad0

flang/lib/Evaluate/variable.cpp

@@ -567,15 +567,7 @@ template <typename T> BaseObject Designator<T>::GetBaseObject() const {
       common::visitors{
           [](SymbolRef symbol) { return BaseObject{symbol}; },
           [](const Substring &sstring) { return sstring.GetBaseObject(); },
-          [](const auto &x) {
-#if !__clang__ && __GNUC__ == 7 && __GNUC_MINOR__ == 2
-            if constexpr (std::is_same_v<std::decay_t<decltype(x)>,
-                              Substring>) {
-              return x.GetBaseObject();
-            } else
-#endif
-              return BaseObject{x.GetFirstSymbol()};
-          },
+          [](const auto &x) { return BaseObject{x.GetFirstSymbol()}; },
       },
       u);
 }
@@ -585,15 +577,7 @@ template <typename T> const Symbol *Designator<T>::GetLastSymbol() const {
       common::visitors{
           [](SymbolRef symbol) { return &*symbol; },
           [](const Substring &sstring) { return sstring.GetLastSymbol(); },
-          [](const auto &x) {
-#if !__clang__ && __GNUC__ == 7 && __GNUC_MINOR__ == 2
-            if constexpr (std::is_same_v<std::decay_t<decltype(x)>,
-                              Substring>) {
-              return x.GetLastSymbol();
-            } else
-#endif
-              return &x.GetLastSymbol();
-          },
+          [](const auto &x) { return &x.GetLastSymbol(); },
       },
       u);
 }

flang/lib/Semantics/symbol.cpp

@@ -733,22 +733,10 @@ bool GenericKind::IsOperator() const {
 
 std::string GenericKind::ToString() const {
   return common::visit(
-      common::visitors {
-        [](const OtherKind &x) { return std::string{EnumToString(x)}; },
-            [](const common::DefinedIo &x) { return AsFortran(x).ToString(); },
-#if !__clang__ && __GNUC__ == 7 && __GNUC_MINOR__ == 2
-            [](const common::NumericOperator &x) {
-              return std::string{common::EnumToString(x)};
-            },
-            [](const common::LogicalOperator &x) {
-              return std::string{common::EnumToString(x)};
-            },
-            [](const common::RelationalOperator &x) {
-              return std::string{common::EnumToString(x)};
-            },
-#else
-            [](const auto &x) { return std::string{common::EnumToString(x)}; },
-#endif
+      common::visitors{
+          [](const OtherKind &x) { return std::string{EnumToString(x)}; },
+          [](const common::DefinedIo &x) { return AsFortran(x).ToString(); },
+          [](const auto &x) { return std::string{common::EnumToString(x)}; },
       },
       u);
 }