syntax-check: fix violations and implement sc_prohibit_test_const_follows_var.

syntax-check: fix violations and implement sc_prohibit_test_const_follows_var.

To safely use a non-literal first argument to `test', you must
always prepend a literal non-`-' character, but often the second
operand is a constant that doesn't begin with a `-' already, so
always use `test a = "$b"' instead of noisy `test "X$b" = Xa'.
* cfg.mk (sc_prohibit_test_const_follows_var): New syntax-check
rule to ensure we don't reintroduce noisy test operands.
* bootstrap, build-aux/extract-trace, build-aux/general.m4sh,
build-aux/ltmain.m4sh, doc/libtool.texi, libtoolize.m4sh,
m4/argz.m4, m4/libtool.m4, m4/ltdl.m4, tests/bindir.at,
tests/defs.m4sh, tests/demo-relink.test,
tests/demo/configure.ac, tests/depdemo-relink.test,
tests/destdir.at, tests/duplicate_conv.at, tests/fail.at,
tests/getopt-m4sh.at, tests/help.at, tests/libtoolize.at,
tests/link-2.test, tests/link-order2.at, tests/lt_dlopenext.at,
tests/mdemo/configure.ac, tests/mdemo2/configure.ac,
tests/need_lib_prefix.at, tests/nocase.at,
tests/pdemo/configure.ac, tests/pic_flag.at,
tests/search-path.at, tests/shlibpath.at, tests/static.at,
tests/sysroot.at, tests/tagtrace.test, tests/testsuite.at,
tests/with-pic.at: Swap operands to avoid useless noise.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>