Remove lisp_h_XCONS etc

Remove lisp_h_XCONS etc

When configured with --enable-checking and compiled with gcc -O0,
these macros evaluated arguments multiple times, which made it too
easy to mistakenly write code that behaves differently when debugging.
This patch does not affect performance in normal builds.
In --enable-checking builds with gcc -O0 it slows down my usual
benchmark (remove all '*.elc’ files and then 'make') by 4.4%.
I hope that’s good enough; if not I can complicate the macros to
tune better for debugging builds.
* src/lisp.h (lisp_h_SET_SYMBOL_VAL, lisp_h_SYMBOL_VAL)
(lisp_h_XCONS): Remove, moving each definiens to the corresponding
inline function.  All uses removed.