lang/ldc: fix runtime on powerpc*

Fixes build of x11-toolkits/gtkd:
ld: error: undefined symbol: __tls_get_addr_opt
>>> referenced by sections_elf_shared.d
>>>               sections_elf_shared.o:(_D2rt19sections_elf_shared3DSO8tlsRangeMxFNbNiZAv) in archive /usr/local/lib/libdruntime-ldc.a
>>> referenced by sections_elf_shared.d
>>>               sections_elf_shared.o:(_D2rt19sections_elf_shared11getTLSRangeFNbNimmmZAv) in archive /usr/local/lib/libdruntime-ldc.a
>>> referenced by sections_elf_shared.d
>>>               sections_elf_shared.o:(_d_dso_registry) in archive /usr/local/lib/libdruntime-ldc.a
>>> referenced 1 more times