Remove prebuild dependency

Every CI build task tagged with 'package' now populates and
publishes the relevant npm/platform directory as an artefact.
These are aggregated by a fan-in release task at the end to
create a complete npm workspace zipfile. If the commit is
tagged, a release is created and the npm workspace attached.

src/binding.gyp

@@ -163,6 +163,8 @@
             },
             'xcode_settings': {
               'OTHER_LDFLAGS': [
+                '-Wl,-s',
+                '-Wl,-dead_strip',
                 # Ensure runtime linking is relative to sharp.node
                 '-Wl,-rpath,\'@loader_path/../../sharp-libvips-<(platform_and_arch)/lib\'',
                 '-Wl,-rpath,\'@loader_path/../../../sharp-libvips-<(platform_and_arch)/<(sharp_libvips_version)/lib\'',
@@ -176,6 +178,9 @@
             'defines': [
               '_GLIBCXX_USE_CXX11_ABI=1'
             ],
+            'cflags_cc': [
+              '<!(node -p "require(\'detect-libc\').isNonGlibcLinuxSync() ? \'\' : \'-flto=auto\'")'
+            ],
             'link_settings': {
               'libraries': [
                 '-l:libvips-cpp.so.<(vips_version)'