Updated code based on PR feedback

Created new functions to capture the different categories of directives.

verible/verilog/parser/verilog-token-classifications.cc

diff --git a/verible/verilog/parser/verilog-token-classifications.cc b/verible/verilog/parser/verilog-token-classifications.cc
index 27ab8ba..1e53ceb 100644
--- a/verible/verilog/parser/verilog-token-classifications.cc
+++ b/verible/verilog/parser/verilog-token-classifications.cc
@@ -92,17 +92,8 @@
   }
 }
 
-bool IsPreprocessorKeyword(verilog_tokentype token_type) {
+bool IsCompilerDirective(verilog_tokentype token_type) {
   switch (token_type) {
-    case verilog_tokentype::PP_include:
-    case verilog_tokentype::PP_define:
-    case verilog_tokentype::PP_ifdef:
-    case verilog_tokentype::PP_ifndef:
-    case verilog_tokentype::PP_else:
-    case verilog_tokentype::PP_elsif:
-    case verilog_tokentype::PP_endif:
-    case verilog_tokentype::PP_undef:
-    // Compiler directives (DR_*)
     case verilog_tokentype::DR_timescale:
     case verilog_tokentype::DR_resetall:
     case verilog_tokentype::DR_celldefine:
@@ -132,6 +123,22 @@
   }
 }
 
+bool IsPreprocessorKeyword(verilog_tokentype token_type) {
+  switch (token_type) {
+    case verilog_tokentype::PP_include:
+    case verilog_tokentype::PP_define:
+    case verilog_tokentype::PP_ifdef:
+    case verilog_tokentype::PP_ifndef:
+    case verilog_tokentype::PP_else:
+    case verilog_tokentype::PP_elsif:
+    case verilog_tokentype::PP_endif:
+    case verilog_tokentype::PP_undef:
+      return true;
+    default:
+      return IsCompilerDirective(token_type);
+  }
+}
+
 bool IsPreprocessorControlToken(verilog_tokentype token_type) {
   switch (token_type) {
     case verilog_tokentype::PP_Identifier:

verible/verilog/parser/verilog-token-classifications.h

diff --git a/verible/verilog/parser/verilog-token-classifications.h b/verible/verilog/parser/verilog-token-classifications.h
index e6109c5..4b15df0 100644
--- a/verible/verilog/parser/verilog-token-classifications.h
+++ b/verible/verilog/parser/verilog-token-classifications.h
@@ -40,6 +40,10 @@
 // Returns true for `ifdef, `define, `include, `undef, etc.
 bool IsPreprocessorKeyword(verilog_tokentype);
 
+// Returns true for SystemVerilog compiler directives (DR_*), e.g. `timescale,
+// `default_nettype, `resetall, etc.
+bool IsCompilerDirective(verilog_tokentype);
+
 // Returns true for any preprocessing token, not just control flow.
 bool IsPreprocessorControlToken(verilog_tokentype token_type);