When cpio 2.13 is built using clang 11.1.0 there's a linking error because of a
duplicate symbol:
```
Making install in src
make[1]: Entering directory
'/Users/toonn/src/nixpkgs/cpio-shell/cpio-2.13/cpio-2.13/src'
CCLD cpio
ld: warning: -sdk_version and -platform_version are not compatible, ignoring
-sdk_version
duplicate symbol '_program_name' in:
global.o
../gnu/libgnu.a(progname.o)
ld: 1 duplicate symbol for architecture x86_64
clang-11: error: linker command failed with exit code 1 (use -v to see
invocation)
make[1]: *** [Makefile:1276: cpio] Error 1
make[1]: Leaving directory
'/Users/toonn/src/nixpkgs/cpio-shell/cpio-2.13/cpio-2.13/src'
make: *** [Makefile:1282: install-recursive] Error 1
post-installation fixup
gzipping man pages under
/nix/store/9rnb8i3nfnjkhmibcwy517xq7ds611vh-cpio-2.13/share/man/
strip is
/nix/store/ihs2dgd42s8h8b35fhv6qmy62vpv65g0-bootstrap-stage0-clang/bin/strip
```
The full linker invocation (I patched `src/Makefile` to pass `-v` in the `CCLD`
definition):
```
"/nix/store/f2cpyzpmqp1j4b0hak27ji1avhr6ijz1-bootstrap-stage0-clang-wrapper-11.1.0/bin/ld"
-demangle -lto_library
/nix/store/7s9ra8gyq839w3fwk9i3jlp97cnd18vi-bootstrap-tools/lib/libLTO.dylib
-dynamic -arch x86_64 -platform_version macos 10.12.0 0.0.0 -o cpio
-L/nix/store/cdmicaw2115h2f4bxlwizsiv21b8ax59-bootstrap-stage0-libcxx/lib
-L/nix/store/hzmh09gf10n90kniphrx6bl3lwg2iqs1-bootstrap-stage0-libcxxabi/lib
-L/nix/store/cdmicaw2115h2f4bxlwizsiv21b8ax59-bootstrap-stage0-libcxx/lib
-L/nix/store/hzmh09gf10n90kniphrx6bl3lwg2iqs1-bootstrap-stage0-libcxxabi/lib
-L/nix/store/dp077zqaqq95qk6jklm2ra2wlvv0k2wh-bootstrap-stage0-Libsystem/lib
-L/nix/store/ihs2dgd42s8h8b35fhv6qmy62vpv65g0-bootstrap-stage0-clang/lib
-sdk_version 10.12 -no_uuid copyin.o copyout.o copypass.o defer.o dstring.o
global.o fatal.o main.o tar.o util.o filemode.o idcache.o makepath.o userspec.o
../lib/libpax.a ../gnu/libgnu.a -lSystem
-F/nix/store/7s9ra8gyq839w3fwk9i3jlp97cnd18vi-bootstrap-tools/Library/Frameworks
```
Previously cpio was being built using clang 7.1.0. I believe the relevant
change is `-fno-common` became a default in clang 11.0.0 as can be read in the
[release
notes](https://releases.llvm.org/11.0.0/tools/clang/docs/ReleaseNotes.html#modified-compiler-flags
<https://releases.llvm.org/11.0.0/tools/clang/docs/ReleaseNotes.html#modified-compiler-flags>).
The build succeeds if I patch the `CC` definition in `src/Makefile` to pass
`-fcommon` (I'm sure there's a better mechanism to do this but I'm not familiar
with the use of CFLAGS).
The [Gentoo Linux GCC 10 porting
notes](https://wiki.gentoo.org/wiki/Gcc_10_porting_notes/fno_common
<https://wiki.gentoo.org/wiki/Gcc_10_porting_notes/fno_common>) may be helpful.
