fix: Passing is_debug to gn

[PerikiyoXD]

I've tried to build v8, failing because a few errors.
I encountered that gn wouldn't take is_debug in some cases, thus needing a ternary check to always pass true or false.

Without fix:

gn.bat gen out.gn "--args=target_cpu=\"x64\" use_custom_libcxx=false target_os=\"win\" is_clang=false treat_warnings_as_errors=false is_official_build=false v8_enable_test_features=false is_shared_library=false is_component_build=false v8_enable_i18n_support=false extra_cflags=[\"/MT\"] v8_monolithic=true v8_use_external_startup_data=false symbol_level=0 v8_static_library=true"

With fix:

gn.bat gen out.gn "--args=v8_enable_test_features=false is_component_build=false treat_warnings_as_errors=false is_clang=false extra_cflags=[\"/MT\"] v8_enable_i18n_support=false is_official_build=false target_cpu=\"x64\" is_shared_library=false symbol_level=0 target_os=\"win\" v8_monolithic=true v8_static_library=true use_custom_libcxx=false is_debug=false v8_use_external_startup_data=false"

Relevant part: is_debug=

It would never put the is_debug=false even if it was defined in the config.

An update to v8 will be posted soon.