inline gtest print support function defns

[wilsonqin]

We have some application code including faster.h, and found that inline definitions for the new gtest print support functions reduce our build situations of linker error for multiple defns. There is a decent chance for collisions on the "<<" operator defn depending on what other c++ libraries are included in the application code.

Linux, C++, g++ 7.4

[badrishc]

Thanks, Wilson. @Skyprophet, any comments?

[dongx-psu]

It is reasonable, I would merge it.

P.s. Modern compilers are usually smart enough to inline them with higher optimization.

[wilsonqin]

@Skyprophet, thank you for the feedback.
I thought compiler optimization would resolve too. Was using -O2 on the application.
In some builds we have a multiple header include - perhaps that could complicate the optimization.