Increase portability to more C++ compilers

src/suffix.h

@@ -16,15 +16,16 @@
 
 namespace LAMMPS_NS {
 
-enum Suffix {
+namespace Suffix {
-  NONE   = 0,
+  enum {
-  OPT    = 1<<0,
+    NONE   = 0,
-  GPU    = 1<<1,
+    OPT    = 1<<0,
-  OMP    = 1<<2,
+    GPU    = 1<<1,
-  INTEL  = 1<<3,
+    OMP    = 1<<2,
-  KOKKOS = 1<<4
+    INTEL  = 1<<3,
-};
+    KOKKOS = 1<<4
-
+  };
+}
 }
 
 #endif