Fix float arithmetic codegen and math_log aliasing

Float + previously fell through to string concat (segfault); -, *, /, %
operated on raw IEEE-754 bit patterns as integers (garbage results). Floats
are now tracked via a __float_names typed-binding set (parallel to the
existing int-tracking scheme) and arithmetic is emitted as real C double
ops.

Also fixes math_log, which was wrongly aliased to natural log (duplicating
math_ln) — now uses log10 — and adds the missing <math.h> include. Rebuilt
elc binary included.

lang/el-compiler/runtime/el_runtime.h

@@ -49,6 +49,7 @@
 
 #include <stdint.h>
 #include <stdlib.h>
+#include <math.h>   /* fmod, sin, sqrt, ... — used by codegen'd float arithmetic */
 
 typedef int64_t el_val_t;