Restructure with separate uclibc branch

src/unix/errors

src/unix/mod.rs

src/unix/notbsd/linux/mips/mips32.rs

src/unix/notbsd/linux/mips/mod.rs

src/unix/notbsd/linux/mod.rs

src/unix/notbsd/linux/notuclibc/mod.rs

src/unix/notbsd/linux/other/mod.rs

src/unix/notbsd/linux/uclibc/mod.rs

src/unix/uclibc/mips/mips32.rs

src/unix/uclibc/mips/mips64.rs

src/unix/uclibc/mips/mod.rs

src/unix/uclibc/mod.rs

src/unix/uclibc/other/b32/arm.rs

src/unix/uclibc/other/b32/mod.rs

src/unix/uclibc/other/b32/powerpc.rs

src/unix/uclibc/other/b32/x86.rs

src/unix/uclibc/other/b64/aarch64.rs

src/unix/uclibc/other/b64/mod.rs

src/unix/uclibc/other/b64/powerpc64.rs

src/unix/uclibc/other/b64/sparc64.rs