Make deps/merve honour --shared-simdutf.

merve.gyp hardcodes the include path of V8's bundled simdutf, with no
condition on node_shared_simdutf. Under --shared-simdutf that makes merve.cpp
compile against the bundled header while linking against the system library.
Any version skew between the two is then a link error: in the bundled 7.7.0
simdutf::find is an exported function, whereas from 9.0.0 on it is an inline
wrapper and only simdutf::detail::find remains in the library, so
node_mksnapshot fails with "undefined reference to simdutf::find".

The condition added here is the one node already uses for simdutf in
node.gypi, so the bundled header is picked up only when simdutf is bundled.

Not accepted upstream -- bentoo does not submit to Gentoo or to node.

--- a/deps/merve/merve.gyp
+++ b/deps/merve/merve.gyp
@@ -8,7 +8,6 @@
       'type': 'static_library',
       'include_dirs': [
         '.',
-        '../v8/third_party/simdutf',
       ],
       'direct_dependent_settings': {
         'include_dirs': ['.'],
@@ -16,6 +15,9 @@
       'defines': [ 'MERVE_USE_SIMDUTF=1' ],
       'sources': [ '<@(merve_sources)' ],
       'conditions': [
+        [ 'node_shared_simdutf=="false" and node_use_bundled_v8!="false"', {
+          'include_dirs': [ '../v8/third_party/simdutf' ],
+        }],
         ['OS=="win"', {
           'msvs_settings': {
             'VCCLCompilerTool': {