Add -fPIC flag using R config PIC variant

[lepennec]

The latest sf version does not compile under fedora: configure yields

checking GDAL: linking with --libs only... yes
checking GDAL: /usr/share/gdal/pcs.csv readable... yes
checking GDAL: checking whether PROJ is available for linking:... no
/usr/bin/ld: /tmp/ccJ892zj.o: relocation R_X86_64_32 against symbol `__gxx_personality_v0@@CXXABI_1.3' can not be used when making a PIE object; recompile with -fPIC
/usr/bin/ld: final link failed: nonrepresentable section on output
collect2: error: ld returned 1 exit status
configure: Install failure: compilation and/or linkage problems.
configure: error: cannot link projection code

Using the PIC version of the FLAGS with R Config solves the issue.

[edzer]

Did you check here?

[rsbivand]

No problem with fully updated Fedora 31, R 4.0.0 beta, and sf from CRAN.

[edzer]

I think this was resolved by adding CXXFLAGS to configure.ac in #1369; let me know if I am wrong.