No available targets are compatible with triple "wasm32-unknown-unknown"

I'm trying to compile an application using flate2 with features = ["zlib-ng-compat",], default-features = false and I'm getting an error:

Install a sysroot for the target platform and configure it via
  PKG_CONFIG_SYSROOT_DIR and PKG_CONFIG_PATH, or install a
  cross-compiling wrapper for pkg-config and set it via
  PKG_CONFIG environment variable.
  TARGET = Some("wasm32-unknown-unknown")
  OPT_LEVEL = Some("3")
  HOST = Some("x86_64-apple-darwin")
  CC_wasm32-unknown-unknown = None
  CC_wasm32_unknown_unknown = None
  TARGET_CC = None
  CC = None
  CFLAGS_wasm32-unknown-unknown = None
  CFLAGS_wasm32_unknown_unknown = None
  TARGET_CFLAGS = None
  CFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("false")
  running: "clang" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "--target=wasm32-unknown-unknown" "-I" "src/zlib" "-fvisibility=hidden" "-DZ_SOLO" "-DSTDC" "-D_LARGEFILE64_SOURCE" "-D_POSIX_SOURCE" "-o" "/Users/samdenty/Projects/isomorphic-git/zlib-wasm/target/wasm32-unknown-unknown/release/build/libz-sys-7094e0907550e67a/out/lib/src/zlib/adler32.o" "-c" "src/zlib/adler32.c"
  cargo:warning=error: unable to create target: 'No available targets are compatible with triple "wasm32-unknown-unknown"'
  cargo:warning=1 error generated

Reproduce the reported flate2 configuration with zlib-ng-compat and default-features disabled for wasm32-unknown-unknown. Start by reading the libz-sys build path and checking the shown clang target invocation; done means the target's compatibility is established with a tested resolution or a clearly documented limitation.