Rename BUILD_FROM_SOURCE to RCT_BUILD_HERMES_FROM_SOURCE

Summary:
In OSS we have reports like [this one](facebook#43241) where env variables from different settings might clash together, making react native apps fail to build hermes.

For example, a team might have defined a BUILD_FROM_SOURCE env variable to build their specific project from source and that will clash with how react native apps installs Hermes.

This change disambiguate the BUILD_FROM_SOURCE flag we have internally, moving to a less likely to clash RCT_BUILD_HERMES_FROM_SOURCE.

## Changelog:
[iOS][Breaking] - Rename BUILD_FROM_SOURCE to RCT_BUILD_HERMES_FROM_SOURCE

Differential Revision: D54356337

.circleci/configurations/executors.yml

@@ -35,11 +35,11 @@ executors:
       xcode: *xcode_version
     resource_class: macos.x86.medium.gen2
     environment:
-      - BUILD_FROM_SOURCE: true
+      - RCT_BUILD_HERMES_FROM_SOURCE: true
   reactnativeios-lts:
     <<: *defaults
     macos:
       xcode: '14.3.1'
     resource_class: macos.x86.medium.gen2
     environment:
-      - BUILD_FROM_SOURCE: true
+      - RCT_BUILD_HERMES_FROM_SOURCE: true

.circleci/configurations/jobs.yml

@@ -599,7 +599,7 @@ jobs:
     environment:
       - HERMES_WS_DIR: *hermes_workspace_root
       - HERMES_VERSION_FILE: "packages/react-native/sdks/.hermesversion"
-      - BUILD_FROM_SOURCE: true
+      - RCT_BUILD_HERMES_FROM_SOURCE: true
     steps:
       - run:
           name: Install dependencies

packages/react-native/sdks/hermes-engine/hermes-utils.rb

@@ -7,6 +7,7 @@
 require 'rexml/document'
 
 HERMES_GITHUB_URL = "https://github.com/facebook/hermes.git"
+ENV_BUILD_FROM_SOURCE = "RCT_BUILD_HERMES_FROM_SOURCE"
 
 module HermesEngineSourceType
     LOCAL_PREBUILT_TARBALL = :local_prebuilt_tarball
@@ -30,7 +31,7 @@ def HermesEngineSourceType.isFromSource(source_type)
 # - To use a specific tarball, install the dependencies with:
 # `HERMES_ENGINE_TARBALL_PATH=<path_to_tarball> bundle exec pod install`
 # - To force a build from source, install the dependencies with:
-# `BUILD_FROM_SOURCE=true bundle exec pod install`
+# `RCT_BUILD_HERMES_FROM_SOURCE=true bundle exec pod install`
 # If none of the two are provided, Cocoapods will check whether there is a tarball for the current version
 # (either release or nightly). If not, it will fall back to building from source (the latest commit on main).
 #
@@ -85,11 +86,11 @@ def hermes_commit_envvar_defined()
 end
 
 def force_build_from_tag(react_native_path)
-    return ENV['BUILD_FROM_SOURCE'] === 'true' && File.exist?(hermestag_file(react_native_path))
+    return ENV[ENV_BUILD_FROM_SOURCE] === 'true' && File.exist?(hermestag_file(react_native_path))
 end
 
 def force_build_from_main(react_native_path)
-    return ENV['BUILD_FROM_SOURCE'] === 'true' && !File.exist?(hermestag_file(react_native_path))
+    return ENV[ENV_BUILD_FROM_SOURCE] === 'true' && !File.exist?(hermestag_file(react_native_path))
 end
 
 def release_artifact_exists(version)