Add arm-uclibc definitions

src/unix/uclibc/arm/align.rs

+s! {
+    // FIXME this is actually a union
+    #[cfg_attr(target_pointer_width = "32",
+               repr(align(4)))]
+    #[cfg_attr(target_pointer_width = "64",
+               repr(align(8)))]
+    pub struct sem_t {
+        #[cfg(target_pointer_width = "32")]
+        __size: [::c_char; 16],
+        #[cfg(target_pointer_width = "64")]
+        __size: [::c_char; 32],
+    }
+}

src/unix/uclibc/arm/no_align.rs

+s! {
+    // FIXME this is actually a union
+    pub struct sem_t {
+        #[cfg(target_pointer_width = "32")]
+        __size: [::c_char; 16],
+        #[cfg(target_pointer_width = "64")]
+        __size: [::c_char; 32],
+        __align: [::c_long; 0],
+    }
+}

src/unix/uclibc/mod.rs

@@ -1893,6 +1893,9 @@ cfg_if! {
     } else if #[cfg(target_arch = "x86_64")] {
         mod x86_64;
         pub use self::x86_64::*;
+    } else if #[cfg(target_arch = "arm")] {
+        mod arm;
+        pub use self::arm::*;
     } else {
         pub use unsupported_target;
     }