Fix coroutine_type variable name

configure.ac

@@ -1098,7 +1098,7 @@ main()
 		AS_IF([test "$target_cpu" = x64], [
 		    ac_cv_func___builtin_setjmp=yes
 		    ac_cv_func_round=no
-		    rb_cv_coroutine=yes
+		    coroutine_type=yes
 		])
 		ac_cv_func_tgamma=no
 		rb_cv_negative_time_t=yes
@@ -4213,7 +4213,7 @@ config_summary "vendor path"         "$vendordir"
 config_summary "target OS"           "$target_os"
 config_summary "compiler"            "$CC"
 config_summary "with pthread"        "$enable_pthread"
-config_summary "with coroutine"      "$rb_cv_coroutine"
+config_summary "with coroutine"      "$coroutine_type"
 config_summary "enable shared libs"  "$ENABLE_SHARED"
 config_summary "dynamic library ext" "$DLEXT"
 config_summary "CFLAGS"              "$cflags"