tests: fix spurious failure with older m4

tests: fix spurious failure with older m4

Reported by Panther Martin in automake bug#10866, diagnosed by
Panther Martin and Eric Blake.

Older GNU m4 versions (e.g., 1.4.6) did error reporting at the end
of an error construct rather than the beginning.  This was causing
a spurious testsuite failure due to an off-by-one error in the line
number reported in an aclocal diagnostic.

* tests/cond41.test: Keep all the body of the 'AM_COND_IF'
invocation on a single line, to avoid the off-by-one error.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>