R installed from buildcache crashes #6418
Description
Cannot use R from buildcache unless the directory path is identical
Expected Result
Running a buildcache-installed R should open an R shell
Actual Result
R crashes because it hard-codes R_HOME and R_{HOME,SHARE,INCLUDE,DOC}_DIR in it's shell wrapper
Steps to reproduce
$ spack buildcache install /ozq2oj7 # An instance of R from buildcache
$ `spack location -i r`/bin/R
<NEW_PATH>/spack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/r-3.4.1-ozq2oj7bwwlhkqncnommq6yfguvovxo2/bin/R: line 238: <OLD_PATH>/spack/opt/spack/linux-centos7-x86_64/gcc-4.8.5/r-3.4.1-ozq2oj7bwwlhkqncnommq6yfguvovxo2/rlib/R/etc/ldpaths: No such file or directoryInformation on your system
Cache created in a Centos 7.4 environment.