[PATCH] tests/testsuite.at: Don't use $as_echo

tests/testsuite.at was using the undocumented internal shell variable
$as_echo to set its own variable $ECHO.  M4sh stopped setting this
variable in a patch committed to autoconf development trunk in January
of 2013, which was mostly harmless since there was a fallback setting
for $ECHO.  As of March 2020, however, merely mentioning $as_echo in
an m4sh input file will trigger a -Wobsolete warning.

The fix is to promote the fallback setting to be the default setting
and not reference $as_echo anymore.  This is safe for the same reason
it was safe for autoconf to stop setting $as_echo -- 'printf %s\n' is a
reliable way to do echoing in all of the shells that are worth worrying
about anymore.
---
 tests/testsuite.at | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tests/testsuite.at b/tests/testsuite.at
index d561c2a4..9e33c75a 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -29,8 +29,7 @@ m4_divert_push([PREPARE_TESTS])dnl
 : ${AUTOCONF=autoconf}
 : ${AUTOMAKE=automake}
 : ${AUTORECONF=autoreconf}
-test set = "${ECHO+set}" || ECHO=${as_echo-'printf %s\n'}
-: ${ECHO=$as_echo}
+: ${ECHO='printf %s\n'}
 for tool in ACLOCAL AUTOHEADER AUTOCONF AUTOMAKE AUTORECONF; do
   if eval \$$tool --version >/dev/null 2>&1; then :; else eval $tool=no; fi
 done
-- 
2.25.1