rgdal compile confusion

And the output of sessionInfo() - we don't know your platform. How was
GDAL itself installed: from source or binary? Was that binary built on the
same platform? Are there multiple GDAL installations on your system? If
so, the configure step may see one version but install sees another.

Roger,

sessionInfo()

R version 3.5.1 (2018-07-02)
Platform: i586-slackware-linux-gnu (32-bit)
Running under: Slackware 14.2

Matrix products: default
BLAS: /usr/lib/R/lib/libRblas.so
LAPACK: /usr/lib/R/lib/libRlapack.so

locale:
  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=C
  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
  [9] LC_ADDRESS=C               LC_TELEPHONE=C 
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] compiler_3.5.1 tools_3.5.1    tcltk_3.5.1

   gdal is built from source using the SlackBuiilds.org
<https://www.slackbuilds.org/> build script.

   gdal-2.3.1 is the only gdal package installed.

   With the upgraded (2.3.0 -> 2.3.1) gdal version installed fails the same
way in response to both update.packages() and install.packages('rgdal'):

install.packages('rgdal')

trying URL 'https://ftp.osuosl.org/pub/cran/src/contrib/rgdal_1.3-4.tar.gz'
Content type 'application/x-gzip' length 1664774 bytes (1.6 MB)
==================================================
downloaded 1.6 MB

* installing *source* package ?rgdal? ...
** package ?rgdal? successfully unpacked and MD5 sums checked
configure: R_HOME: /usr/lib/R
configure: CC: gcc
configure: CXX: g++
configure: C++11 support available
configure: rgdal: 1.3-4
checking for /usr/bin/svnversion... yes
configure: svn revision: 766
checking for gdal-config... /usr/bin/gdal-config
checking gdal-config usability... yes
configure: GDAL: 2.3.1
checking C++11 support for GDAL >= 2.3.0... yes
checking GDAL version >= 1.11.4... yes
checking gdal: linking with --libs only... no
checking gdal: linking with --libs and --dep-libs... no
In file included from /usr/include/gdal.h:45:0,
                  from gdal_test.cc:1:
/usr/include/cpl_port.h:187:6: error: #error Must have C++11 or newer.
  #    error Must have C++11 or newer.
       ^
In file included from /usr/include/gdal.h:49:0,
                  from gdal_test.cc:1:
/usr/include/cpl_minixml.h:202:47: error: expected template-name before '<' token
  class CPLXMLTreeCloser: public std::unique_ptr<CPLXMLNode, CPLXMLTreeCloserDeleter>
                                                ^
/usr/include/cpl_minixml.h:202:47: error: expected '{' before '<' token
/usr/include/cpl_minixml.h:202:47: error: expected unqualified-id before '<' token
In file included from /usr/include/ogr_api.h:45:0,
                  from /usr/include/gdal.h:50,
                  from gdal_test.cc:1:
/usr/include/ogr_core.h:79:28: error: expected '}' before end of line
/usr/include/ogr_core.h:79:28: error: expected declaration before end of line
In file included from /usr/include/gdal.h:45:0,
                  from gdal_test.cc:1:
/usr/include/cpl_port.h:187:6: error: #error Must have C++11 or newer.
  #    error Must have C++11 or newer.
       ^
In file included from /usr/include/gdal.h:49:0,
                  from gdal_test.cc:1:
/usr/include/cpl_minixml.h:202:47: error: expected template-name before '<' token
  class CPLXMLTreeCloser: public std::unique_ptr<CPLXMLNode, CPLXMLTreeCloserDeleter>
                                                ^
/usr/include/cpl_minixml.h:202:47: error: expected '{' before '<' token
/usr/include/cpl_minixml.h:202:47: error: expected unqualified-id before '<' token
In file included from /usr/include/ogr_api.h:45:0,
                  from /usr/include/gdal.h:50,
                  from gdal_test.cc:1:
/usr/include/ogr_core.h:79:28: error: expected '}' before end of line
/usr/include/ogr_core.h:79:28: error: expected declaration before end of line
configure: Install failure: compilation and/or linkage problems.
configure: error: GDALAllRegister not found in libgdal.
ERROR: configuration failed for package ?rgdal?
* removing ?/usr/lib/R/library/rgdal?
* restoring previous ?/usr/lib/R/library/rgdal?

The downloaded source packages are in
 	?/tmp/RtmpfJQHZG/downloaded_packages?
Updating HTML index of packages in '.Library'
Making 'packages.html' ... done
Warning message:
In install.packages("rgdal") :
   installation of package ?rgdal? had non-zero exit status

   What other information can I provide?

Regards,

Rich