Skip installing optional npm deps, but manually install Closure Compiler native package (#636)

Follow on to #625, #630, #632, #633
Fixes emscripten-core/emscripten#12406

emsdk.py

@@ -1223,13 +1223,41 @@ def emscripten_npm_install(tool, directory):
   print('Running post-install step: npm ci ...')
   try:
     subprocess.check_output(
-        [npm, 'ci', '--production'],
+        [npm, 'ci', '--production', '--no-optional'],
         cwd=directory, stderr=subprocess.STDOUT, env=env,
         universal_newlines=True)
   except subprocess.CalledProcessError as e:
     print('Error running %s:\n%s' % (e.cmd, e.output))
     return False
 
+  # Manually install the appropriate native Closure Compiler package
+  # This is currently needed because npm ci will install the packages
+  # for Closure for all platforms, adding 180MB to the download size
+  # There are two problems here:
+  #   1. npm ci does not consider the platform of optional dependencies
+  #      https://github.com/npm/cli/issues/558
+  #   2. A bug with the native compiler has bloated the packages from
+  #      30MB to almost 300MB
+  #      https://github.com/google/closure-compiler-npm/issues/186
+  # If either of these bugs are fixed then we can remove this exception
+  closure_compiler_native = ''
+  if LINUX and ARCH in ('x86', 'x86_64'):
+    closure_compiler_native = 'google-closure-compiler-linux'
+  if MACOS and ARCH in ('x86', 'x86_64'):
+    closure_compiler_native = 'google-closure-compiler-osx'
+  if WINDOWS and ARCH == 'x86_64':
+    closure_compiler_native = 'google-closure-compiler-windows'
+  if closure_compiler_native:
+    print('Running post-install step: npm install', closure_compiler_native)
+    try:
+      subprocess.check_output(
+        [npm, 'install', closure_compiler_native],
+        cwd=directory, stderr=subprocess.STDOUT, env=env,
+        universal_newlines=True)
+    except subprocess.CalledProcessError as e:
+      print('Error running %s:\n%s' % (e.cmd, e.output))
+      return False
+
   print('Done running: npm ci')
   return True