Revert "Optimize vswap()"

This reverts commit 63193d1794.

Had some problems (_STATIC_ASSERT) and was too ugly anyway.
For retry, I'd suggest to implement a general function
    static inline void memswap (void *p1, void* p2, size_t n);
and then use that.  If you do so, please keep the original code
as comment.

tcc.h

@@ -228,10 +228,6 @@
 #define true 1
 typedef int BOOL;
 
-#ifndef _STATIC_ASSERT
-#define _STATIC_ASSERT(cond) do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)
-#endif
-
 #define INCLUDE_STACK_SIZE  32
 #define IFDEF_STACK_SIZE    64
 #define VSTACK_SIZE         256