gcc80: Make LTO plugins installation consistent.

Previously my LTO additions were (ab)using bug in bsd.lib.mk.
All other cases in world override both variables.
Do the same fix for gcc47 too.

No fu

gcc80: Make LTO plugins installation consistent.

Previously my LTO additions were (ab)using bug in bsd.lib.mk.
All other cases in world override both variables.
Do the same fix for gcc47 too.

No functional change intended.

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gcc80: Add pregenerated manpages.

gcc80: Add pregenerated headers.

gcc80: Bring in makefiles but leave them unhooked.

Makefile infrastructure was reused from gcc50 one writen by John Marino.