Docs: Add clang path for Windows ARM64 hosts

[joseluisq]

This PR just adds a new clang path to the BUILDING.md when the host is a Windows ARM64.

It was tested by building a Rust project using ring 0.17.5 on a Windows 11 ARM64 (M1 Parallels VM) successfully.

Otherwise, I should get an error similar to the following:

ring-0.17.5\build.rs:673:9:
  failed to execute ["clang" "-O3" "--target=aarch64-pc-windows-msvc" "-ffunction-sections" "-fdata-sections" "--target=aarch64-pc-windows-msvc" "-I" "include" "-I" "C:\\Users\\joseluisq\\devel\\static-web-server\\target\\aarch64-pc-windows-msvc\\release\\build\\ring-400e2572fe09d335\\out" "-Wall" "-Wextra" "-fvisibility=hidden" "-std=c1x" "-pedantic" "-Wall" "-Wextra" "-Wbad-function-cast" "-Wcast-align" "-Wcast-qual" "-Wconversion" "-Wenum-compare" "-Wfloat-equal" "-Wformat=2" "-Winline" "-Winvalid-pch" "-Wmissing-field-initializers" "-Wmissing-include-dirs" "-Wnested-externs" "-Wredundant-decls" "-Wshadow" "-Wsign-compare" "-Wsign-conversion" "-Wstrict-prototypes" "-Wundef" "-Wuninitialized" "-Wwrite-strings" "-g3" "-DNDEBUG" "-c" "-oC:\\Users\\joseluisq\\devel\\static-web-server\\target\\aarch64-pc-windows-msvc\\release\\build\\ring-400e2572fe09d335\\out\\aesv8-armx-win64.o" "C:\\Users\\joseluisq\\.cargo\\registry\\src\\index.crates.io-6f17d22bba15001f\\ring-0.17.5\\pregenerated\\aesv8-armx-win64.S"]: program not found

[briansmith]

Thanks!

[briansmith]

BTW, you may be interested in rust-lang/cc-rs#882, which proposes to automate this away.

[joseluisq]

BTW, you may be interested in rust-lang/cc-rs#882, which proposes to automate this away.

Thanks! I didn't know about that. That improvement should be great.