(AC_SYNCLINES_COMPILE): Accept any nonzero

exit status as failure, not just exit status 1.  Sun C exits
with status 2 sometimes.

tests/synclines.at

@@ -24,7 +24,7 @@ AT_BANNER([[User Actions.]])
 # Compile FILE expecting an error, and save in the file stdout the normalized
 # output.
 m4_define([AT_SYNCLINES_COMPILE],
-[AT_CHECK([$CC $CFLAGS $CPPFLAGS $1 -c], 1, [], [stderr])
+[AT_CHECK([$CC $CFLAGS $CPPFLAGS -c $1 || (exit 1)], 1, [], [stderr])
 # In case GCC displays column information, strip it down.
 #
 #   input.y:4:2: #error "4"    or input.y:4.2: #error "4"