re PR java/43839 (libjava incorrectly uses -liconv in testsuite, jni.exp when using --with-libiconv-prefix)

	PR 43839
	* testsuite/Makefile.am: Override automake for site.exp creation
	and add entry to set libiconv.
	* testsuite/Makefile.in: Regenerate.
	* testsuite/libjava.jni/jni.exp (gcj_jni_get_cxxflags_invocation):
	Add new global variable libiconv to handle alternative libiconv
	locations.

From-SVN: r159009