Revert "Suppress occasional autoconf warnings"

This reverts commit 32bfb61, that
requires autoconf 2.70's improved whitespace handling.  It is too
early for some platforms yet.

Fix rubyGH-13910

Author: nobu

configure.ac

@@ -2815,12 +2815,12 @@ AS_IF([test "$THREAD_MODEL" = pthread], [
     ], [
 	AC_DEFINE(NON_SCALAR_THREAD_ID)
     ])
-    AC_CHECK_FUNCS([sched_yield pthread_attr_setinheritsched
-	pthread_attr_get_np pthread_attr_getstack pthread_attr_getguardsize
-	pthread_get_stackaddr_np pthread_get_stacksize_np
-	thr_stksegment pthread_stackseg_np pthread_getthrds_np
-	pthread_condattr_setclock
-	pthread_setname_np pthread_set_name_np])
+    AC_CHECK_FUNCS(sched_yield pthread_attr_setinheritsched \
+	pthread_attr_get_np pthread_attr_getstack pthread_attr_getguardsize \
+	pthread_get_stackaddr_np pthread_get_stacksize_np \
+	thr_stksegment pthread_stackseg_np pthread_getthrds_np \
+	pthread_condattr_setclock \
+	pthread_setname_np pthread_set_name_np)
     AS_CASE(["$target_os"],[emscripten*],[ac_cv_func_pthread_sigmask=no],[AC_CHECK_FUNCS(pthread_sigmask)])
     AS_CASE(["$target_os"],[aix*],[ac_cv_func_pthread_getattr_np=no],[AC_CHECK_FUNCS(pthread_getattr_np)])
     set_current_thread_name=