[CI Infrastructure] R-MKLDNN-CPU test run failure. gcc fails due to ccache issue?

[DickJC123]

Description

During the work on PR #19298, the following CI job failed in the windows-cpu R-MKLDNN-CPU test job: https://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-cpu/detail/PR-19298/1/pipeline/304/. This doesn't appear related to the PR, but more with the CI infrastructure and its use of ccache. Despite the failure being part of the 'test running' phase, gcc was invoked. See below for relevant error message.

A retry of this job did not repeat the error.

Error Message

...
[2020-10-06T07:47:24.018Z] gcc -std=gnu99 -I/usr/share/R/include -DNDEBUG     -Iutf8lite/src -fpic  -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -g  -c utf8lite/src/render.c -o utf8lite/src/render.o
...
[2020-10-06T07:47:24.018Z] ccache: error: /work/ccache/ccache.conf: No such file or directory
[2020-10-06T07:47:24.018Z] make[1]: *** [render.o] Error 1
[2020-10-06T07:47:24.018Z] make[1]: *** Waiting for unfinished jobs....
[2020-10-06T07:47:24.018Z] /usr/lib/R/etc/Makeconf:159: recipe for target 'render.o' failed

[leezu]

In v1.x branch, there is a global ccache configuration:

https://github.com/apache/incubator-mxnet/blob/3b69c607b611eb8f275aa8ed512a380ac0fd768d/ci/docker/runtime_functions.sh#L63-L111

We can just remove it's invocation in the R language tests:

https://github.com/apache/incubator-mxnet/blob/3b69c607b611eb8f275aa8ed512a380ac0fd768d/ci/docker/runtime_functions.sh#L1186-L1191

If that slows down the R test stage too much, one can investigate updating the R toolchain.

[leezu]

Closed via #19305

[DickJC123]

Awesome, thanks for the quick turnaround!