[clang] Support -fpic -fno-semantic-interposition for AArch64
-fno-semantic-interposition (only effective with -fpic) can optimize default visibility external linkage (non-ifunc-non-COMDAT) variable access and function calls to avoid GOT/PLT, by using local aliases, e.g. ``` int var; __attribute__((optnone)) int fun(int x) { return x * x; } int test() { return fun(var); } ``` -fpic (var and fun are dso_preemptable) ``` test: // @test adrp x8, :got:var ldr x8, [x8, :got_lo12:var] ldr w0, [x8] // fun is preemptible by default in ld -shared mode. ld will create a PLT. b fun ``` vs -fpic -fno-semantic-interposition (var and fun are dso_local) ``` test: // @test .Ltest$local: adrp x8, .Lvar$local ldr w0, [x8, :lo12:.Lvar$local] // The assembler either resolves .Lfun$local at assembly time, or produces a // relocation referencing a non-preemptible section symbol (which can avoid PLT). b .Lfun$local ``` Note: Clang's default -fpic is more aggressive than GCC -fpic: interprocedural optimizations (including inlining) are available but local aliases are not used. -fpic -fsemantic-interposition can disable interprocedural optimizations. Depends on D101872 Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D101873
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