Static Hermes for React Native

[piaskowyk]

Summary

This PR introduces necessary changes to let React Native uses latest version of static Hermes.

Explanation

Part 1

set(OVERRIDE_HERMES_MOBILE_BUILD OFF CACHE BOOL "Workaround for Android builds that use ES types defined conditionally")
if (OVERRIDE_HERMES_MOBILE_BUILD)
  set(HERMES_IS_MOBILE_BUILD OFF)
endif()

The HERMES_IS_MOBILE_BUILD flag is only set when the HERMES_IS_ANDROID flag is active. However, these two have different roles. To correctly build for Android, I need the flexibility to set these flags separately. This is crucial because the HERMES_IS_MOBILE_BUILD flag might lead to build failures if there are undeclared types being used - an issue we've already flagged to the Hermes team (I can create an issue with a description if you wants)

Part 2

append("/d2UndefIntOverflow-" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)

It seems like this flag doesn’t exist anymore in the MSVC 16 compiler.
CI logs - https://github.com/piaskowyk/react-native/actions/runs/11815096269/job/32915591004

fatal error C1007: unrecognized flag '-UndefIntOverflow-' in 'p2'

Part 3

if("${CMAKE_CXX_COMPILER_ID}" MATCHES "MSVC")
  # MSVC needs C++20
  set(CMAKE_CXX_STANDARD 20)
else()
  set(CMAKE_CXX_STANDARD 17)
endif()

Some of the new syntax in static Hermes requires the newer C++ standard on MSVC.

Part 4

# Changes in lib/CMakeLists.txt

These updates are necessary to successfully build the Hermes Framework for iOS.

Part 5

namespace hermes {
namespace hbc {
namespace {

class BytecodeSerializer {
-  friend void visitBytecodeSegmentsInOrder<BytecodeSerializer>(
+  friend void hermes::hbc::visitBytecodeSegmentsInOrder<BytecodeSerializer>(

Due to additional additional anonymous namespace, the MSVC wasn't able to recognise proper symbol without explicite definition.

Test Plan

Build RNTester app from here - https://github.com/piaskowyk/react-native/tree/%40piaskowyk/build-static-hermes