Add support for tail calls

[nunoplopes]

We have positives in GVN because of missing support for tail calls.
see, e.g.: llvm/llvm-project#61670
https://alive2.llvm.org/ce/z/GssD2L

define i64 @src(i64 noundef %arg) {
  %call2 = alloca i64
  %call3 = alloca i64
  store i64 %arg, ptr %call2, align 8
  tail call void @llvm.memcpy.p0.p0.i64(ptr %call3, ptr %call2, i64 8, i1 false)
  %load1 = load i64, ptr %call3, align 8
  ret i64 %load1
}

declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg)

$ opt -p gvn
define i64 @src(i64 %arg) {
  %call2 = alloca i64, align 8
  %call3 = alloca i64, align 8
  store i64 %arg, ptr %call2, align 8
  tail call void @llvm.memcpy.p0.p0.i64(ptr %call3, ptr %call2, i64 8, i1 false)
  ret i64 undef
}