* configure.in: Test for Autoconf >= 2.52.

* configure.in: Test for Autoconf >= 2.52.
* tests/defs (needs_autoconf, has_autoconf): Delete definition.
* tests/ansi3.test, tests/ansi5.test, tests/ccnoco.test,
tests/cond4.test, tests/cond9.test, tests/cond16.test,
tests/cond18.test, tests/cond19.test, tests/cond20.test,
tests/confsub.test, tests/depcomp2.test, tests/depdist.test,
tests/depend2.test, tests/dirname.test, tests/distname.test,
tests/extra5.test, tests/install2.test, tests/lex3.test,
tests/make.test, tests/nobase.test, tests/pr9.test,
tests/pr87.test, tests/stamph2.test, tests/subdir5.test,
tests/subdirbuiltsources.test, tests/subobj3.test,
tests/subobj5.test, tests/subobj6.test, tests/substref.test,
tests/target-cflags.test, tests/yacc4.test, tests/yacc7.test,
tests/yaccvpath.test: Do not use $needs_autoconf.