Add round-mode context support to sparc.

	* sysdeps/sparc/fpu/fenv_private.h (HAVE_RM_CTX): Define.
	(libc_feholdexcept_setround_sparc_ctx): New function.
	(libc_fesetenv_sparc_ctx): Likewise.
	(libc_feupdateenv_sparc_ctx): Likewise.
	(libc_feholdsetround_sparc_ctx): Likewise.
	(libc_feholdexcept_setround_ctx): Define.
	(libc_feholdexcept_setroundf_ctx): Likewise.
	(libc_feholdexcept_setroundl_ctx): Likewise.
	(libc_fesetenv_ctx): Likewise.
	(libc_fesetenvf_ctx): Likewise.
	(libc_fesetenvl_ctx): Likewise.
	(libc_feupdateenv_ctx): Likewise.
	(libc_feupdateenvf_ctx): Likewise.
	(libc_feupdateenvl_ctx): Likewise.
	(libc_feresetround_ctx): Likewise.
	(libc_feresetroundf_ctx): Likewise.
	(libc_feresetroundl_ctx): Likewise.
	(libc_feholdsetround_ctx): Likewise.
	(libc_feholdsetroundf_ctx): Likewise.
	(libc_feholdsetroundl_ctx): Likewise.