[ELF] - Fixed bug leading to miss of tls relocation when @tlsgd and @gottpoff...

[ELF] - Fixed bug leading to miss of tls relocation when @tlsgd and @gottpoff relocations were used at the same time.

Combination of @tlsgd and @gottpoff at the same time leads to miss of R_X86_64_TPOFF64 dynamic relocation. Patch fixes that.

@tlsgd(%rip) - Allocate two contiguous entries in the GOT to hold a tls index
structure (for passing to tls get addr).
@gottpoff(%rip) - Allocate one GOT entry to hold a variable offset in initial TLS
block (relative to TLS block end, %fs:0).

The same situation can be observed for x86 (probably others too, not sure) with corresponding for that target relocations: @tlsgd, @gotntpoff.

Differential revision: http://reviews.llvm.org/D15105

llvm-svn: 254443