Remove unique attribute from section.

A non-zero constant initialized thread_local does not emit this with Clang
(https://godbolt.org/z/PjddWeb57) and it is not understood by older assemblers.
Fixes #222.

PiperOrigin-RevId: 672542340
Change-Id: I7cd54a2252b1b5d8830ba574277c6ac8e4f1a626

tcmalloc/internal/percpu_rseq_asm.S

@@ -36,7 +36,7 @@
 .type tcmalloc_cached_vcpu, @object
 .type tcmalloc_slabs, @object
 .type __rseq_abi, @object
-.section .tdata, "awT", @progbits, unique, 1
+.section .tdata, "awT", @progbits
 .globl tcmalloc_sampler
 .globl tcmalloc_cached_vcpu
 .globl tcmalloc_slabs