Build of sf on RHEL7 fails: ./configure: line 3769: Linux: command not found (Linux is the output of `uname`)

[pascalgulikers]

Building the sf package on RHEL7 fails due to this change, PR: https://github.com/r-spatial/sf/pull/1702/files. I made a new PR which resolves the issue: https://github.com/r-spatial/sf/pull/1712

* installing *source* package ‘sf’ ...
** package ‘sf’ successfully unpacked and MD5 sums checked
** using staged installation
configure: CC: gcc -m64 -std=gnu99
configure: CXX: g++ -m64 -std=gnu++11
checking for gdal-config... /usr/gdal30/bin/gdal-config
checking gdal-config usability... yes
configure: GDAL: 3.0.4
checking GDAL version >= 2.0.1... yes
checking for gcc... gcc -m64 -std=gnu99
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc -m64 -std=gnu99 accepts -g... yes
checking for gcc -m64 -std=gnu99 option to accept ISO C89... none needed
checking how to run the C preprocessor... gcc -m64 -std=gnu99 -E
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking gdal.h usability... yes
checking gdal.h presence... yes
checking for gdal.h... yes
checking GDAL: linking with --libs only... yes
checking GDAL: /usr/gdal30/share/pcs.csv readable... no
checking GDAL: checking whether PROJ is available for linking:... yes
checking GDAL: checking whether PROJ is available fur running:... yes
configure: GDAL: 3.0.4
configure: pkg-config proj exists, will use it
configure: using proj.h.
./configure: line 3769: Linux: command not found
configure: PROJ: 7.0.0
checking PROJ: checking whether PROJ and sqlite3 are available for linking:... no
configure: error: libproj or sqlite3 not found in standard or given locations.
ERROR: configuration failed for package ‘sf’
* removing ‘/data/share/R/library/sf’
* restoring previous ‘/data/share/R/library/sf’

[pascalgulikers]

@edzer