Add support for specifying fixed RTK base position

And fix build error…

-GIT_TAG is redundant
-closes #4023

* travis-ci try ccache on OSX and android

* travis-ci ccache stats

* try again

* Attempt to prepend ccache to qmake command

* Test enabling ccache for ios too

* Deploy ccache from S3 per @dagar

* Revert "Test enabling ccache for ios too"

It was a nice thought.

This reverts commit 7e7aeb367696ee9c8abc5cc8122dcd35196d96bb.

* Try to optimally set the number of make jobs

* Fix job estimation and disable ccache on android

* Android: reenable ccache and disable parallel jobs

* Check if android build passes with 4 workers

* Try to parallelize xcodebuild too

* Give mac builders an extra worker and pretty up the ios build output

* Add make output filtering with correct exit code, no sudo or ccache on ios build

* Try wrapping ccache to enable use on xcodebuild

* Make ios ccache helpers executable

* Turn back on pretty printing for IOS

* Show some ccache stats on IOS build to see if we're getting hits

* Change android build OS type to linux

* Require trusty for android build

* Require sudo for android so we get trusty

* Maybe this will function properly on edge?

* Try to use stripped binary bzips

* Screw it! Run android on precise again

* Back to the original android build configuration. I give up

* [WIP] deploy release and daily build pdbs to s3

* First pass at windows symbol generation for #2680

* Kill the conflicted compiler flag warning

* Tweaks to windows compiler flags for release builds, more qt-ish release symbols and ltcg

* Deploy tagged release symbols and CI builds to different S3 folders

* Support LTCG on iOS

* Just turn off ltcg for iOS if it is going to be such a pain

Allows QGC to run on Raspberry Pi 2 with direct framebuffer (X/startx
not needed). Memory split seems to need 128 for GPU. Qt5 needs to be
configured with "-opengl es2 -qpa eglfs -device linux-rasp-pi2-g++".