Make more improvements

This change includes many bug fixes, for the NT polyfills, strings,
memory, boot, and math libraries which were discovered by adding more
tools for recreational programming, such as PC emulation. Lemon has also
been vendored because it works so well at parsing languages.

libc/log/backtrace3.c

@@ -31,6 +31,16 @@
 #include "libc/stdio/stdio.h"
 #include "libc/str/str.h"
 
+/**
+ * Prints stack frames with symbols.
+ *
+ *   PrintBacktraceUsingSymbols(stdout, NULL, getsymboltable());
+ *
+ * @param f is output stream
+ * @param bp is rbp which can be NULL to detect automatically
+ * @param st is open symbol table for current executable
+ * @return -1 w/ errno if error happened
+ */
 int PrintBacktraceUsingSymbols(FILE *f, const struct StackFrame *bp,
                                struct SymbolTable *st) {
   size_t gi;
@@ -41,6 +51,7 @@ int PrintBacktraceUsingSymbols(FILE *f, const struct StackFrame *bp,
   const struct Symbol *symbol;
   const struct StackFrame *frame;
   if (!st) return -1;
+  if (!bp) bp = __builtin_frame_address(0);
   garbage = weaken(g_garbage);
   gi = garbage ? garbage->i : 0;
   for (frame = bp; frame; frame = frame->next) {