Fix and improve G-code queue (#21122)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/core/macros.h

@@ -349,6 +349,31 @@
   #define CALL_IF_EXISTS(Return, That, Method, ...) \
     static_cast<Return>(Private::Call_ ## Method(That, ##__VA_ARGS__))
 
+  // Compile-time string manipulation
+  namespace CompileTimeString {
+    // Simple compile-time parser to find the position of the end of a string
+    constexpr const char* findStringEnd(const char *str) {
+      return *str ? findStringEnd(str + 1) : str;
+    }
+
+    // Check whether a string contains a slash
+    constexpr bool containsSlash(const char *str) {
+      return *str == '/' ? true : (*str ? containsSlash(str + 1) : false);
+    }
+    // Find the last position of the slash
+    constexpr const char* findLastSlashPos(const char* str) {
+      return *str == '/' ? (str + 1) : findLastSlashPos(str - 1);
+    }
+    // Compile-time evaluation of the last part of a file path
+    // Typically used to shorten the path to file in compiled strings
+    // CompileTimeString::baseName(__FILE__) returns "macros.h" and not /path/to/Marlin/src/core/macros.h
+    constexpr const char* baseName(const char* str) {
+      return containsSlash(str) ? findLastSlashPos(findStringEnd(str)) : str;
+    }
+  }
+
+  #define ONLY_FILENAME CompileTimeString::baseName(__FILE__)
+
 #else
 
   #define MIN_2(a,b)      ((a)<(b)?(a):(b))