library/std/build.rs: "powerpc64le" is not a target_arch

The target_arch of `powerpc64le` is `powerpc64`, so
`powerpc64le` can be removed from a match arm in build.rs
related to f16.

You can check available `target_arch`:s with:

    $ rustc +nightly -Zunstable-options --print all-target-specs-json \
            | grep powerpc | grep arch | sort | uniq
        "arch": "powerpc",
        "arch": "powerpc64",

std/build.rs

@@ -99,7 +99,7 @@ fn main() {
         // the compiler-builtins update. <https://github.com/rust-lang/rust/issues/123885>
         ("x86" | "x86_64", _) => false,
         // Missing `__gnu_h2f_ieee` and `__gnu_f2h_ieee`
-        ("powerpc" | "powerpc64" | "powerpc64le", _) => false,
+        ("powerpc" | "powerpc64", _) => false,
         // Missing `__extendhfsf` and `__truncsfhf`
         ("riscv32" | "riscv64", _) => false,
         // Most OSs are missing `__extendhfsf` and `__truncsfhf`