btar: add -fcommon workaround

Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:

ld: listindex.o:/build/btar-1.1.1/loadindex.h:12: multiple definition of
`ptr'; main.o:/build/btar-1.1.1/loadindex.h:12: first defined here

+6
+6
pkgs/tools/backup/btar/default.nix
··· 16 16 }) 17 17 ]; 18 18 19 + # Workaround build failure on -fno-common toolchains like upstream 20 + # gcc-10. Otherwise build fails as: 21 + # ld: listindex.o:/build/btar-1.1.1/loadindex.h:12: multiple definition of 22 + # `ptr'; main.o:/build/btar-1.1.1/loadindex.h:12: first defined here 23 + NIX_CFLAGS_COMPILE = "-fcommon"; 24 + 19 25 buildInputs = [ librsync ]; 20 26 21 27 makeFlags = [ "PREFIX=$(out)" ];