atomics: cleanup HAVE_ATOMICS define

The waf build system generates this already. No point in redoing it in
the header file.

The legacy build system (which we really should drop) didn't; fix it.

TOOLS/old-configure

@@ -514,9 +514,12 @@ check_statement_libs "compiler support for __sync built-ins" $_sync SYNC_BUILTIN
     stdint.h 'int64_t test = 0; test = __sync_add_and_fetch(&test, 1)'
 _sync=$(defretval)
 
+_any_atomic=yes
 if test "$_atomic" = no && test "$_sync" = no && test "$_stdatomic" = no ; then
   echo "your compiler must support either stdatomic.h, or __atomic, or __sync built-ins."
+  _any_atomic=no
 fi
+define_yes_no $_any_atomic HAVE_ATOMICS
 
 check_compile "iconv" $_iconv ICONV waftools/fragments/iconv.c " " "-liconv" "-liconv $_ld_dl"
 _iconv=$(defretval)

osdep/atomics.h

@@ -22,8 +22,6 @@
 #include <inttypes.h>
 #include "config.h"
 
-#define HAVE_ATOMICS 1
-
 #if HAVE_STDATOMIC
 #include <stdatomic.h>
 #else
@@ -97,9 +95,6 @@ typedef struct { volatile unsigned long long v, t;  } atomic_ullong;
 #define atomic_compare_exchange_strong(p, old, new) \
     ((p)->v == *(old) ? ((p)->v = (new), 1) : (*(old) = (p)->v, 0))
 
-#undef HAVE_ATOMICS
-#define HAVE_ATOMICS 0
-
 #endif /* no atomics */
 
 #endif /* else HAVE_STDATOMIC */