Using -flto in CXXFLAGS_FOR_TARGET

[U.Mutlu]

I tried to use -flto in CXXFLAGS_FOR_TARGET. It successfully built the compilers,
but later when trying to use the compilers, the linker reported an error about 
something missing and aborted the linking.

Of course the rationale was to optimize the compiler itself.

So, the question is: does it not make any sense to use -flto for the build itself?
(Or should one specify -flto in some of the other config variables like 
CXXFLAGS_FOR_BUILD and/or the ...FLAGS vars maybe?)

Thx