[flang][NFC] Fix header guards

Some header guards conflicted with clang. Fix a few others to follow the
convention in the rest of the headers in flang.

Author: tarunprabhu

flang/include/flang/Common/Version.h

@@ -12,8 +12,8 @@
 ///
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_FLANG_COMMON_VERSION_H
-#define LLVM_FLANG_COMMON_VERSION_H
+#ifndef FORTRAN_COMMON_VERSION_H
+#define FORTRAN_COMMON_VERSION_H
 
 #include "flang/Version.inc"
 #include "llvm/ADT/StringRef.h"
@@ -53,4 +53,4 @@ std::string getFlangFullVersion();
 std::string getFlangToolFullVersion(llvm::StringRef ToolName);
 } // namespace Fortran::common
 
-#endif // LLVM_FLANG_COMMON_VERSION_H
+#endif // FORTRAN_COMMON_VERSION_H

flang/include/flang/Frontend/CodeGenOptions.h

@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_CLANG_BASIC_CODEGENOPTIONS_H
-#define LLVM_CLANG_BASIC_CODEGENOPTIONS_H
+#ifndef FORTRAN_FRONTEND_CODEGENOPTIONS_H
+#define FORTRAN_FRONTEND_CODEGENOPTIONS_H
 
 #include "llvm/Frontend/Debug/Options.h"
 #include "llvm/Frontend/Driver/CodeGenOptions.h"
@@ -141,4 +141,4 @@ class CodeGenOptions : public CodeGenOptionsBase {
 
 } // end namespace Fortran::frontend
 
-#endif
+#endif // FORTRAN_FRONTEND_CODEGENOPTIONS_H

flang/include/flang/Frontend/LangOptions.h

@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_FLANG_FRONTEND_LANGOPTIONS_H
-#define LLVM_FLANG_FRONTEND_LANGOPTIONS_H
+#ifndef FORTRAN_FRONTEND_LANGOPTIONS_H
+#define FORTRAN_FRONTEND_LANGOPTIONS_H
 
 #include <string>
 
@@ -63,4 +63,4 @@ class LangOptions : public LangOptionsBase {
 
 } // end namespace Fortran::frontend
 
-#endif
+#endif // FORTRAN_FRONTEND_LANGOPTIONS_H