feat(libzigc): add common linux errno syscall helper

lib/c/common.zig

@@ -13,3 +13,17 @@ pub const visibility: std.builtin.SymbolVisibility = if (linkage != .internal)
     .hidden
 else
     .default;
+
+/// Checks whether the syscall has had an error, storing it in `std.c.errno` and returning -1.
+/// Otherwise returns the result.
+pub fn linuxErrno(r: usize) isize {
+    const linux = std.os.linux;
+
+    return switch (linux.errno(r)) {
+        .SUCCESS => @bitCast(r),
+        else => |err| blk: {
+            std.c._errno().* = @intFromEnum(err);
+            break :blk -1;
+        },
+    };
+}

lib/c/sys/utsname.zig

@@ -13,15 +13,7 @@ comptime {
 }
 
 fn unameLinux(uts: *std.os.linux.utsname) callconv(.c) c_int {
-    const linux = std.os.linux;
-
-    return switch (linux.errno(linux.uname(uts))) {
-        .SUCCESS => 0,
-        else => |err| blk: {
-            std.c._errno().* = @intFromEnum(err);
-            break :blk -1;
-        },
-    };
+    return @intCast(common.linuxErrno(std.os.linux.uname(uts)));
 }
 
 fn unameWasi(uts: *std.c.utsname) callconv(.c) c_int {