COMP: compilation with clang (c++17) and older flex files (fixes #3337)

- The register keyword has been removed from c++17 but old flex
  versions (version < 2.6.0) produce code including it, leading to
  compilation errors when using clang (despite disabling the diagnostic).
  gcc compiles but issues warnings.

- use '#define register' as empty as a workaround

applications/utilities/mesh/conversion/ansysToFoam/ansysToFoam.L

@@ -62,6 +62,9 @@ Description
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 using namespace Foam;
 

applications/utilities/mesh/conversion/fluent3DMeshToFoam/fluent3DMeshToFoam.L

@@ -56,6 +56,9 @@ Description
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

applications/utilities/mesh/conversion/fluentMeshToFoam/fluentMeshToFoam.L

@@ -63,6 +63,9 @@ Description
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 

applications/utilities/mesh/conversion/gambitToFoam/gambitToFoam.L

@@ -51,6 +51,9 @@ Description
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 using namespace Foam;
 

src/fileFormats/stl/STLAsciiParseFlex.L

@@ -44,6 +44,9 @@ Description
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 using namespace Foam;
 

src/thermophysicalModels/reactionThermo/chemistryReaders/chemkinReader/chemkinLexer.L

@@ -39,6 +39,9 @@ License
 
 // Flex may use register, which is deprecated and incompatible with C++17
 #pragma clang diagnostic ignored "-Wdeprecated-register"
+// A 'nothing' define to effectively remove from code as well (issue #3337)
+#undef  register
+#define register
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //