Tweak up compile flags

- Remove unnecessary `-x c++`.
 - Improve rebuild speed by caching:
   - Remove `-f` from `autoreconf` to reuse generated configure scripts.
   - Remove `--rm` from `docker run` to avoid rebuilding Emscripten stdlib.
   - Add `-C` to `./configure` to reuse stored information about `emcc`.
   - Remove `rm -rf build` from WebP encoder/decoder.

codecs/mozjpeg_enc/build.sh

@@ -15,9 +15,9 @@ echo "Compiling mozjpeg"
 echo "============================================="
 (
   cd node_modules/mozjpeg
-  autoreconf -fiv
-  emconfigure ./configure --without-simd
-  emmake make libjpeg.la -j`nproc`
+  autoreconf -iv
+  emconfigure ./configure -C --without-simd
+  emmake make libjpeg.la rdswitch.o -j`nproc`
 )
 echo "============================================="
 echo "Compiling mozjpeg done"
@@ -31,18 +31,15 @@ echo "============================================="
     --bind \
     ${OPTIMIZE} \
     --closure 1 \
-    -s WASM=1 \
     -s ALLOW_MEMORY_GROWTH=1 \
     -s MODULARIZE=1 \
     -s 'EXPORT_NAME="mozjpeg_enc"' \
     -I node_modules/mozjpeg \
     -o ./mozjpeg_enc.js \
-    -Wno-deprecated-register \
-    -Wno-writable-strings \
-    node_modules/mozjpeg/rdswitch.c \
-    -x c++ -std=c++11 \
+    -std=c++11 \
     mozjpeg_enc.cpp \
-    node_modules/mozjpeg/.libs/libjpeg.a
+    node_modules/mozjpeg/.libs/libjpeg.a \
+    node_modules/mozjpeg/rdswitch.o
 )
 echo "============================================="
 echo "Compiling wasm bindings done"