configure.ac: Fix “too many arguments” error

If GHC_PKG_QUICKCHECK contains multiple values, the test would fail
with “too many arguments”.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

configure.ac

@@ -450,7 +450,7 @@ AC_SUBST(HTOOLS_APIDOC)
 fi # end if enable_htools, define automake conditions
 
 AM_CONDITIONAL([WANT_HTOOLS], [test x$HTOOLS = xyes])
-AM_CONDITIONAL([WANT_HTOOLSTESTS], [test x$GHC_PKG_QUICKCHECK != x])
+AM_CONDITIONAL([WANT_HTOOLSTESTS], [test "x$GHC_PKG_QUICKCHECK" != x])
 AM_CONDITIONAL([WANT_HTOOLSAPIDOC], [test x$HTOOLS_APIDOC = xyes])
 
 SOCAT_USE_ESCAPE=