Linking to libatomic required on 32-bit platforms

[barracuda156]

* installing *source* package ‘qs’ ...
** using staged installation
checking for pkg-config... /opt/local/bin/pkg-config
zstd 1.5.4 library detected -- skipping zstd compilation
lz4 1.9.4 library detected -- skipping lz4 compilation
configure: creating ./config.status
config.status: creating src/Makevars
** libs
/opt/local/bin/g++-mp-12 -std=gnu++14 -I"/opt/local/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -DRCPP_USE_UNWIND_PROTECT -DRCPP_NO_RTTI -DRCPP_NO_SUGAR -I. -I/opt/local/include -I/opt/local/include  -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/Rcpp/include' -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/RApiSerialize/include' -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/stringfish/include' -isystem/opt/local/include/LegacySupport -I/opt/local/include   -fPIC  -pipe -Os -arch ppc  -c RcppExports.cpp -o RcppExports.o
/opt/local/bin/g++-mp-12 -std=gnu++14 -I"/opt/local/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -DRCPP_USE_UNWIND_PROTECT -DRCPP_NO_RTTI -DRCPP_NO_SUGAR -I. -I/opt/local/include -I/opt/local/include  -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/Rcpp/include' -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/RApiSerialize/include' -I'/opt/local/Library/Frameworks/R.framework/Versions/4.2/Resources/library/stringfish/include' -isystem/opt/local/include/LegacySupport -I/opt/local/include   -fPIC  -pipe -Os -arch ppc  -c qs_functions.cpp -o qs_functions.o
/opt/local/bin/g++-mp-12 -std=gnu++14 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/opt/local/Library/Frameworks/R.framework/Resources/lib -Wl,-headerpad_max_install_names -Wl,-rpath,/opt/local/lib/libgcc -L/opt/local/lib -lMacportsLegacySupport -arch ppc -o qs.so RcppExports.o qs_functions.o -L. -lpthread -L/opt/local/lib -lzstd -L/opt/local/lib -llz4 -F/opt/local/Library/Frameworks/R.framework/.. -framework R -Wl,-framework -Wl,CoreFoundation
installing to /opt/local/var/macports/build/_opt_PPCRosettaPorts_R_R-qs/R-qs/work/qs/qs.Rcheck/00LOCK-qs/00new/qs/libs
** R
** data
*** moving datasets to lazyload DB
** inst
** byte-compile and prepare package for lazy loading
** help
*** installing help indices
** building package indices
** installing vignettes
** testing if installed package can be loaded from temporary location
Error: package or namespace load failed for ‘qs’ in dyn.load(file, DLLpath = DLLpath, ...):
 unable to load shared object '/opt/local/var/macports/build/_opt_PPCRosettaPorts_R_R-qs/R-qs/work/qs/qs.Rcheck/00LOCK-qs/00new/qs/libs/qs.so':
  dlopen(/opt/local/var/macports/build/_opt_PPCRosettaPorts_R_R-qs/R-qs/work/qs/qs.Rcheck/00LOCK-qs/00new/qs/libs/qs.so, 6): Symbol not found: ___atomic_store_8
  Referenced from: /opt/local/var/macports/build/_opt_PPCRosettaPorts_R_R-qs/R-qs/work/qs/qs.Rcheck/00LOCK-qs/00new/qs/libs/qs.so
  Expected in: dynamic lookup

Error: loading failed
Execution halted
ERROR: loading failed
* removing ‘/opt/local/var/macports/build/_opt_PPCRosettaPorts_R_R-qs/R-qs/work/qs/qs.Rcheck/qs’

[barracuda156]

The fix would be passing -latomic in Makevars.in conditional on GCC being the compiler and, preferably, on 32-bit platform (or implementing a test for atomics with/without libatomic). Otherwise it is IMO acceptable to link it just conditional on GCC.

[Enchufa2]

Linking to libatomic seems to be required only in some architectures. So far, only this one has been identified (well, not entirely; we would need further details about your platform, @barracuda156), and therefore the inclusion of -latomic should be restricted to this platform to avoid breaking other setups that were working perfectly fine.

[barracuda156]

@Enchufa2 AFAIK, ppc, arm and mips need this for 32-bit versions of archs. I can only test ppc personally, no hardware for the rest. My platform is Darwin.

A quick googling shows that the issue is nothing specific to my platform though:
protocolbuffers/protobuf#5219
arvidn/libtorrent#5117

[barracuda156]

e5bb578 will likely fail to have a desired effect, since we need to check specifically 8-byte atomics.