Do not use open64 on linux with musl

glibc is providing open64 and other lfs64 functions but musl aliases
them to normal equivalents since off_t is always 64-bit on musl,
therefore check for target env along when target OS is linux before
using open64, this is more available. Latest Musl has made these
namespace changes [1]

[1] https://git.musl-libc.org/cgit/musl/commit/?id=246f1c811448f37a44b41cd8df8d0ef9736d95f4

Signed-off-by: Khem Raj <raj.khem@gmail.com>

src/util_libc.rs

@@ -139,7 +139,7 @@ impl Weak {
 }
 
 cfg_if! {
-    if #[cfg(any(target_os = "linux", target_os = "emscripten"))] {
+    if #[cfg(any(all(target_os = "linux", not(target_env = "musl")), target_os = "emscripten"))] {
         use libc::open64 as open;
     } else {
         use libc::open;