Add a definititon of EM_CURRENT for s390x. (#145)

Author: sunfishcode

src/elf.rs

@@ -70,6 +70,8 @@ pub const EM_CURRENT: u16 = 40; // EM_ARM
 pub const EM_CURRENT: u16 = 3; // EM_386
 #[cfg(target_arch = "powerpc64")]
 pub const EM_CURRENT: u16 = 21; // EM_PPC64
+#[cfg(target_arch = "s390x")]
+const EM_CURRENT: u16 = 22; // EM_S390
 #[cfg(any(
     target_arch = "mips",
     target_arch = "mips32r6",