* config/sparc/sol2.h (CPLUSPLUS_CPP_SPEC): Define.

	* porting.texi: Correct documentation about handling
	_LARRGEFILE_SOURCE and its ilk.
	* config/os/solaris/solaris2.5/bits/os_defines.h: Remove
	definitions of _XOPEN_SOURCE, _LARGEFILE64_SOURCE, and
	__EXTENSIONS__.
	* config/os/solaris/solaris2.6/bits/os_defines.h: Likewise.
	* config/os/solaris/solaris2.7/bits/os_defines.h: Likewise.

From-SVN: r42125