Upstream Support for flto plugin with automake

[Patrick Venture]

Only one recipe currently uses flto-automake which provides for the
gcc-ar and gcc-ranlib replacements to build with the flto option.
IIRC, James added this because phosphor-pid-control required them to
compile.  Many (if not all) Makefiles in openbmc pass in the flto
option, and seem to compile fine.

I did some light documentation reading on this feature and as I
understand it, when objects are compiled with this they're left in a
state to improve final "total optimization" during linking.  So,
perhaps in the cases where it compiles without the flto-automake swap
it's not actually able to take advantage of this during compilation?

I ran into an issue today while debugging an SDK issue:
x86_64-openbmc-linux-ar:
.libs/libupdater.lax/libfirmware_common.a/libfirmware_common_la-sys.o:
plugin needed to handle lto object
x86_64-openbmc-linux-ar:
.libs/libupdater.lax/libfirmware_common.a/libfirmware_common_la-util.o:
plugin needed to handle lto object
x86_64-openbmc-linux-ranlib:
.libs/libupdater.a(libfirmware_common_la-sys.o): plugin needed to
handle lto object
x86_64-openbmc-linux-ranlib:
.libs/libupdater.a(libfirmware_common_la-util.o): plugin needed to
handle lto object

This was with phosphor-ipmi-flash, building for the tool.  When
building for the BMC library it also builds those objects, but does so
without issue.  It seems to detect it automatically or favor it
already:

checking for arm-openbmc-linux-gnueabi-ar... (cached)
arm-openbmc-linux-gnueabi-gcc-ar
checking for archiver @FILE support... @
checking for arm-openbmc-linux-gnueabi-strip... (cached)
arm-openbmc-linux-gnueabi-strip
checking for arm-openbmc-linux-gnueabi-ranlib...
arm-openbmc-linux-gnueabi-gcc-ranlib

So it seems flto-automake is obsolete?

If that's the case, I can 1) drop the change from phosphor-pid-control
(the only user) and 2) drop the bbclass.

However, I was wondering what in the SDK could be used to inform it.
I ended up getting past this by adding the information to the
configure line, and that worked fine.

Patrick