Add runtime linker path to pkg-config files

[nigoroll]

Otherwise libraries will not be found at runtime when installing to a path not included in the default runtime linker's path with programs linking brotli configured via pkg-config.

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[nigoroll]

I signed it!

[googlebot]

CLAs look good, thanks!

[nigoroll]

the travis failure looks quite unrelated to me

[AppVeyorBot]

✅ Build brotli 1.0.0#1409 completed (commit 2c73bc0072 by @nigoroll)

[AppVeyorBot]

✅ Build brotli 1.0.0#1413 completed (commit 323233de1e by @nigoroll)

[eustas]

Thanks. Sorry for super-long delay...

[eustas]

Please rebase. Travis will be happy this time.

[nigoroll]

rebased

[AppVeyorBot]

✅ Build brotli 1.0.0#1421 completed (commit ee76fe0e36 by @nigoroll)

[eustas]

Super. Thanks!

[DimStar77]

GCC 10 seems not to be really happy with this. When building libsoup for example, I get:

[ 30s] cc: error: unrecognized command-line option ‘-R’

[Vogtinator]

#836 got opened for that failure