[google gcc-4.9] FDO build for linux kernel

[Rong Xu]

Here is patch that ports our work on FDO linux kernel build support to
gcc-4_9. With this patch, kernel will use the libgcov functions to
dump the gcda files.

This patch also enables LIPO build. But the module grouping is not
computed online. We will use gcov-tool to do this offline.

Tested with kernel FDO build, regression and google internal benchmarks.

Thanks,

-Rong

kfdo_patch
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