Handle different versions of Solaris 8 <iso/math_iso.h>, <iso/stdlib_iso.h>

	* acinclude.m4 (GLIBCXX_CHECK_MATH_PROTO)
	(GLIBCXX_CHECK_STDLIB_PROTO): New tests.
	* configure.ac (GLIBCXX_CHECK_MATH_PROTO)
	(GLIBCXX_CHECK_STDLIB_PROTO): Call them.
	* configure: Regenerate.
	* config.h.in: Regenerate.
	* config/os/solaris/solaris2.8/os_defines.h
	(__CORRECT_ISO_CPP_MATH_H_PROTO2): Don't define.
	* config/os/solaris/solaris2.9: Remove.
	* configure.host (solaris2.8): Merge with ...
	(solaris2.9, solaris2.1[0-9]): ... this.
	Always use os/solaris/solaris2.8.

From-SVN: r178217