[LinuxCNC/linuxcnc PR#556] Misc fixes: Travis CI ccache; .gitignore test artifacts

#1 – zultron 于 2019-02-01

Two builds, same code:
– [ccache not yet primed][2] build time 18:11 (average is more typically around 17+)
– [ccache primed][1] build time 14:37

So it probably shaved off a few minutes from the build. At the end of the log it prints out the cache stats:

“
$ ccache -s
cache directory /home/travis/.ccache
cache hit (direct) 389
cache hit (preprocessed) 3
cache miss 3
called for link 193
called for preprocessing 181
compile failed 1
bad compiler arguments 2
autoconf compile/link 25
no input file 10
files in cache 1166
cache size 62.7 Mbytes
max cache size 512.0 Mbytes
“

[1]: https://travis-ci.org/LinuxCNC/linuxcnc/builds/487412520
[2]: https://travis-ci.org/LinuxCNC/linuxcnc/builds/487405194

#2 – zultron 于 2019-02-01

Tests pass, ready for review. Thanks!