Fix _AS_DETECT_BETTER_SHELL breakage

Problem reported by Zack Weinberg in:
https://lists.gnu.org/r/autoconf/2020-03/msg00017.html
* lib/m4sugar/m4sh.m4 (_AS_RUN): Use sh -c instead of
the no-longer-existent $as_echo.  This fixes a bug introduced
in 2013-01-28T03:44:45Z!gary@gnu.org.

diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index f8be31861f70c5de803e994358ec0b8d6a5b8e70..92999f588b7c50ff3be88768aa7f175e785ad307 100644 (file)
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -418,7 +418,7 @@ m4_default_quoted([$4], [M4SH-INIT-FN]))])])
 # or under the given SHELL, protecting it from syntax errors.
 # Set as_run in order to assist _AS_LINENO_WORKS.
 m4_define([_AS_RUN],
-[m4_ifval([$2], [{ $as_echo "$as_bourne_compatible"$1 | as_run=a $2; }],
+[m4_ifval([$2], [as_run=a $2 -c "$as_bourne_compatible"$1],
                [(eval $1)]) 2>/dev/null])