build.sh: honor EXTRA_CFLAGS env var for per-build static-lib flags

Used by the craftax parity harness to compile with
-DCRAFTAX_JAX_PARITY, which disables the update_mobs early-out so the
C env replays bitwise against JAX. Default training builds leave
EXTRA_CFLAGS empty and keep the ~2x sim-SPS early-out enabled.

Author: Infatoshi

build.sh

@@ -239,7 +239,7 @@ if [ ! -f "$BINDING_SRC" ]; then
 fi
 
 echo "Compiling static library for $ENV..."
-${CC:-clang} -c "${CLANG_OPT[@]}" \
+${CC:-clang} -c "${CLANG_OPT[@]}" $EXTRA_CFLAGS \
     -I. -Isrc -I$SRC_DIR -Ivendor \
     -I./$RAYLIB_NAME/include -I$CUDA_HOME/include \
     -DPLATFORM_DESKTOP \