Rebased on https://patch-diff.githubusercontent.com/raw/ruby/ruby/pull/2995.patch
which was originally based on this file.

--- a/configure.ac
+++ b/configure.ac
@@ -2441,7 +2441,10 @@ AS_CASE([$rb_cv_coroutine], [yes|''], [
             rb_cv_coroutine=copy
         ],
         [
-            rb_cv_coroutine=ucontext
+            AC_CHECK_FUNCS([getcontext swapcontext makecontext],
+                [rb_cv_coroutine=ucontext],
+                [rb_cv_coroutine=copy; break]
+            )
         ]
     )
     AC_MSG_RESULT(${rb_cv_coroutine})