build: fix compiling addons with older versions of Node.js

`common.gypi` is used by `node-gyp` to compile addons. Default values
must be provided for variables that may not exist on older versions of
Node.js so that older versions of Node.js can be used to compile addons
for later versions of Node.js.

Add default values for `v8_enable_pointer_compression` and
`v8_enable_31bit_smis_on_64bit_arch`.

PR-URL: nodejs#33688
Refs: nodejs#30463
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Signed-off-by: Richard Lau <riclau@uk.ibm.com>

common.gypi

@@ -57,6 +57,12 @@
     # https://github.com/nodejs/node/pull/22920/files#r222779926
     'v8_enable_handle_zapping': 0,
 
+    # Disable pointer compression. Can be enabled at build time via configure
+    # options but default values are required here as this file is also used by
+    # node-gyp to build addons.
+    'v8_enable_pointer_compression%': 0,
+    'v8_enable_31bit_smis_on_64bit_arch%': 0,
+
     # Disable V8 untrusted code mitigations.
     # See https://github.com/v8/v8/wiki/Untrusted-code-mitigations
     'v8_untrusted_code_mitigations': 0,