Initial import of libdpf.

Co-authored-by: Cursor <cursoragent@cursor.com>

thirdparty/portable-snippets/debug-trap/README.md

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+# Debugging assertions and traps
+
+This is an attempt to provide a fairly portable way to generate traps
+in code. `__builtin_trap` is `_Noreturn`, so the compiler may optimize
+away code found after it, which means you can't really drop into a
+debugger and step through the code after the trap has been hit.
+
+If `PSNIP_NDEBUG` is defined, or `NDEBUG` is defined and `PSNIP_DEBUG`
+is not, `psnip_dbg_assert(expr)` will be preprocessed to nothing
+(i.e., `expr` will not be evaluated). Otherwise it will call
+`psnip_trap` if `expr` evaluates to false.
+
+Knowledge about how to do this portably basically comes from:
+
+ * [scottt/debugbreak](https://github.com/scottt/debugbreak/).
+ * GLib's [G_BREAKPOINT](https://developer.gnome.org/glib/stable/glib-Warnings-and-Assertions.html#G-BREAKPOINT:CAPS) macro.
+ * [TI's Wiki](http://processors.wiki.ti.com/index.php/Software_Breakpoints_in_the_IDE)
+ * Assorted compiler documentation.
+
+On non-hosted platforms we *may* have to fall back on
+`__builtin_trap`. On non-hosted non-GNU-compatible compilers on
+relatively exotic architectures you may end up with an error about
+stdlib.h being missing... if you have a good way to resolve that on
+your platform please contact us.