[preproc] support C23 enum underlying type syntax (#2043)

tools/preproc/asm_file.cpp

@@ -524,6 +524,17 @@ bool AsmFile::ParseEnum()
     long enumCounter = 0;
     long symbolCount = 0;
 
+    if (m_buffer[m_pos] == ':') // : <type>
+    {
+        m_pos++;
+        std::string underlyingType;
+        do {
+            currentHeaderLine += SkipWhitespaceAndEol();
+            underlyingType = ReadIdentifier();
+        } while (!underlyingType.empty());
+        currentHeaderLine += SkipWhitespaceAndEol();
+    }
+
     if (m_buffer[m_pos] != '{') // assume assembly macro, otherwise assume enum and report errors accordingly
     {
         m_pos = fallbackPosition - 4;