Error needed/conflicts configuration
The purpose is to clarify the error if there is a needed/conflicts
configuration at compile time.
MODIFY
mrbgems/mruby-bin-debugger/tools/mrdb/mrdbconf.h
mrbgems/mruby-bin-debugger/tools/mrdb/mrdbconf.h
#ifndef MRDBCONF_H
#define MRDBCONF_H
+#ifndef MRB_ENABLE_DEBUG_HOOK
+# error Need 'MRB_ENABLE_DEBUG_HOOK' configuration in your 'build_config.rb'
+#endif
+
/* configuration options: */
/* maximum size for command buffer */
#define MAX_COMMAND_LINE 1024

MODIFY
mrbgems/mruby-math/src/math.c
mrbgems/mruby-math/src/math.c
** See Copyright Notice in mruby.h
*/
+#ifdef MRB_WITHOUT_FLOAT
+# error Conflict 'MRB_WITHOUT_FLOAT' configuration in your 'build_config.rb'
+#endif
+
#include <mruby.h>
#include <mruby/array.h>

MODIFY
mrbgems/mruby-random/src/random.c
mrbgems/mruby-random/src/random.c
** See Copyright Notice in mruby.h
*/
+#ifdef MRB_WITHOUT_FLOAT
+# error Conflict 'MRB_WITHOUT_FLOAT' configuration in your 'build_config.rb'
+#endif
+
#include <mruby.h>
#include <mruby/variable.h>
#include <mruby/class.h>

MODIFY
mrbgems/mruby-range-ext/src/range.c
mrbgems/mruby-range-ext/src/range.c
+#ifdef MRB_WITHOUT_FLOAT
+# error Conflict 'MRB_WITHOUT_FLOAT' configuration in your 'build_config.rb'
+#endif
+
#include <mruby.h>
#include <mruby/range.h>
#include <math.h>

MODIFY
mrbgems/mruby-time/src/time.c
mrbgems/mruby-time/src/time.c
** See Copyright Notice in mruby.h
*/
+#ifdef MRB_WITHOUT_FLOAT
+# error Conflict 'MRB_WITHOUT_FLOAT' configuration in your 'build_config.rb'
+#endif
+
#include <math.h>
#include <time.h>
#include <mruby.h>

Error needed/conflicts configuration

The purpose is to clarify the error if there is a needed/conflicts
configuration at compile time.