title: ROracle package installation failure
body: <p>I'm aware of the other questions about this issue, but they don't have much in common with my system setup or the installation error I'm getting, so:</p>
  
  <p>I am using Windows 7, 64 bit</p>
  
  <p>I have installed the 64 bit Oracle Instant Client 18.3.0.0.0 along with its sdk and odbc extensions, available from <a href="http://www.oracle.com/technetwork/topics/winx64soft-089540.html" rel="noreferrer">http://www.oracle.com/technetwork/topics/winx64soft-089540.html</a> </p>
  
  <p>I've put the install location `C:\Oracle\instantclient_18_3' on the PATH.</p>
  
  <p>I have installed R 3.5.1 and Rtools 3.5; both are on the PATH.</p>
  
  <p>In R, </p>
  
  <pre><code>Sys.setenv(
    'ORACLE_HOME' = 'C:/Oracle/instantclient_18_3',
    'OCI_INC'     = 'C:/Oracle/instantclient_18_3/sdk/include',
    'OCI_LIB64'   = 'C:/Oracle/instantclient_18_3'
    )
  install.packages("ROracle", type="source")
  </code></pre>
  
  <p>results in the following</p>
  
  <pre><code>* installing *source* package 'ROracle' ...
  ** package 'ROracle' successfully unpacked and MD5 sums checked
  Oracle Client Shared Library 64-bit - 18.3.0.0.0 Operating in Instant Client mode.
  found Oracle Client C:/Oracle/instantclient_18_3
  found Oracle Client include C:/Oracle/instantclient_18_3/sdk/include
  copying from C:/Oracle/instantclient_18_3/sdk/include
  ** libs
  c:/Rtools/mingw_64/bin/gcc  -I"C:/Program Files/R/R-3.5.1/include" -DNDEBUG -I./oci         -O2 -Wall  -std=gnu99 -mtune=generic -c rodbi.c -o rodbi.o
  In file included from rooci.h:75:0,
                   from rodbi.c:181:
  ./oci/oci.h:716:20: fatal error: ociver.h: No such file or directory
   #include &lt;ociver.h&gt;
                      ^
  compilation terminated.
  make: *** [C:/Program Files/R/R-3.5.1/etc/x64/Makeconf:208: rodbi.o] Error 1
  ERROR: compilation failed for package 'ROracle'
  * removing 'C:/Users/obrienle/Documents/R/win-library/3.5/ROracle'
  In R CMD INSTALL
  Warning in install.packages :
    installation of package ‘ROracle’ had non-zero exit status
  </code></pre>
  
  <p>The file ociver.h that Rtools can't locate is definitely present in the <code>OCI_INC</code> folder, so I don't know why this is happening. Does anyone have any ideas about what to try?</p>