fix(build): define _BSD_SOURCE

System endian conversion macros are gated behind this feature flag for
older versions of GLIBC. `_BSD_SOURCE` and `_SVID_SOURCE` were
deprecated and replaced with `_DEFAULT_SOURCE` starting with GLIBC 2.19.

crates/xtask/src/build_wasm.rs

@@ -199,6 +199,7 @@ pub fn run_wasm(args: &BuildWasm) -> Result<()> {
         "-D", "NDEBUG=",
         "-D", "_POSIX_C_SOURCE=200112L",
         "-D", "_DEFAULT_SOURCE=",
+        "-D", "_BSD_SOURCE=",
         "-D", "_DARWIN_C_SOURCE=",
         "-I", "lib/src",
         "-I", "lib/include",