deps.labjack: support building for windows

The only pthread functionality this seems to use is mutexes, which are
(fortunately) theoretically trivial to wrap for windows. This
compiles, though it is not clear if it actually works correctly.

deps/labjack/ljacklm/build.zig

@@ -17,6 +17,10 @@ pub fn build(b: *std.Build) !void {
         .link_libc = true,
     });
 
+    if (target.result.os.tag == .windows) {
+        libljacklm.defineCMacro("LJACKLM_USE_WINDOWS_MUTEX_SHIM", "1");
+    }
+
     libljacklm.addCSourceFile(.{ .file = b.path("libljacklm/ljacklm.c") });
     libljacklm.installHeader(b.path("libljacklm/ljacklm.h"), "ljacklm.h");